Introduction

This section presents topics included in the analysis of the Happy Isles Gauging Station Bridge Removal Project Environmental Assessment and a rationale for their inclusion. Topics were selected based on federal law, regulations, and executive orders; National Park Service management policies; and concerns expressed by the public, park staff, or other agencies during scoping and comment periods. This section also provides a discussion of topics that were dismissed from further analysis.

A short rationale for each impact topic considered in this chapter is given below. A description of the existing conditions for each selected topic is provided later in this chapter. The affected environment described in this chapter encompasses the geographical area affected by the alternatives. The potential impacts of each alternative within each topic area are presented in Chapter IV, Environmental Consequences.

Impact Topics Considered in this Assessment

Natural Resources

The federal and state Endangered Species Acts (and associated legislation), Clean Water Act, Clean Air Act, and National Environmental Policy Act require that the effects of any federal undertaking on natural resources be examined. In addition, the National Park Service management policies and natural resource management guidelines call for the consideration of natural resources in planning proposals. Significant natural resources, such as special-status species, exist within the park and could be affected by implementation of the alternatives.

Happy Isles Gauging Station Bridge is located on the Merced Wild and Scenic River within Yosemite National Park, in east Yosemite Valley – an area of abundant natural resources. It is therefore necessary to characterize these natural resources and the environmental consequences to these resources that would result from implementation of Happy Isles Gauging Station Bridge Removal Project alternatives.

Analysis was performed for the following natural resource topics:

·      Geology, Geologic Hazards, and Soils

·      Hydrology, Floodplains, and Water Quality

·      Wetlands

·      Vegetation

·      Wildlife

·      Special-Status Species

·      Air Quality

·      Noise

Cultural Resources

The National Historic Preservation Act, the Archeological Resources Protection Act, Native American Graves Protection and Repatriation Act, and the National Environmental Policy Act require that the effects of any federal undertaking on cultural resources be examined. In addition, National Park Service management policies and cultural resource management guidelines call for the consideration of cultural resources in planning proposals. The Happy Isles Gauging Station Bridge is a historic resource and a contributing element within the Yosemite Valley Cultural Landscape. The bridge is also a cultural Outstandingly Remarkable Value, and is discussed in Chapter V, Merced Wild and Scenic River.

Analysis was performed for the following cultural resource topics:

·      Archeological Resources

·      Ethnographic Resources

·      Cultural Landscape Resources, including Historic Sites and Structures

Social Resources

Analysis of social resources examines the effects of the Happy Isles Gauging Station Bridge Removal Project on the social environment in Yosemite Valley. The park’s scenic resources are a major component of the park visitor’s experience. Conserving the scenery is a crucial component of the National Park Service 1916 Organic Act and the park’s enabling legislation. Stewardship of Yosemite National Park requires consideration of two integrated purposes: to preserve Yosemite’s unique natural and cultural resources and scenic beauty, and to make these resources available to visitors for study, enjoyment, and recreation. Implementation of the Happy Isles Gauging Station Bridge Removal Project has potential to affect the type and quality of recreation in the immediate vicinity of the bridge in Yosemite Valley. In addition, the proposed project raises public health and safety concerns that require analysis. The Happy Isles Gauging Station Bridge Removal Project could affect park operations and facilities, such as the water supply line adjacent to the bridge.

Analysis was performed for the following social resource topics:

·      Scenic Resources

·      Recreation

·      Park Operations and Facilities

Impact Topics Dismissed from Further Analysis

Transportation

The Happy Isles Gauging Station Bridge is a pedestrian bridge and has been closed to the public since 1997. The removal of the Happy Isles Gauging Station Bridge would not affect traffic flows in Yosemite Valley. Transportation has been dismissed from further analysis in this environmental assessment.

Land Use

Land uses within Yosemite National Park are classified as “Parklands,” regardless of the individual types of land uses that occur within the park. The removal of the Happy Isles Gauging Station Bridge would not affect the Parklands land use within Yosemite Valley.

Wilderness Experience

There is no designated Wilderness in the immediate project vicinity. The Happy Isles Gauging Station Bridge Removal Project would not have any direct or indirect effects to designated Wilderness.

Socioeconomics

The Happy Isles Gauging Station Bridge Removal Project is a small, localized project in east Yosemite Valley. No aspect of any alternative of the Happy Isles Gauging Station Bridge Removal Project would result in effects to the regional economy, local economy, or the park concessioner.

Environmental Justice

Environmental justice analyses determine whether a proposed action would have “disproportionately high and adverse human health or environmental effects...on minority populations and low-income populations.” The National Park Service and other federal agencies have determined that a disproportionately high and adverse effect on minority and low-income populations means an adverse effect that:

(1)  is predominately borne by a minority population and/or a low-income population, or

(2)  will be suffered by the minority population and/or low-income population and is appreciably more severe or greater in magnitude than the adverse effect that will be suffered by the non-minority population and/or non-low-income population.

No aspect of any alternative of the Happy Isles Gauging Station Bridge Removal Project would result in disproportionately high and adverse human health or environmental effects on minority or low-income populations.

Prime and Unique Agricultural Lands

There are no agricultural lands in the area of potential effect for the Happy Isles Gauging Station Bridge Removal Project, nor would the proposed action have indirect effects on downstream agricultural lands. Thus, no further discussion of this topic is necessary.

Regional Setting

Yosemite National Park lies on the western slope of the Sierra Nevada, a massive mountain range dividing central and northern California from more arid lands to the east. The Sierra Nevada is the highest and most continuous mountain range in California, extending approximately 450 miles north to south and averaging approximately 100 miles wide. Elevations in the park range from approximately 2,000 to 13,114 feet. The total area within the park’s authorized boundary is 747,969 acres.

The Sierra Nevada range contains the headwaters of 24 major river basins, two of which are in the park: the Merced River and the Tuolumne River. In 1984, Congress established portions of the main stem of the Tuolumne River, and the Dana and Lyell Forks, as part of the National Wild and Scenic Rivers System. In 1987, the Wild and Scenic Rivers Act was amended to include 114 miles of both the main stem and South Fork of the Merced River as Wild and Scenic.

The Merced River flows from the headwaters in the high elevations of the Sierra Nevada, through Yosemite Valley, and down to the San Joaquin Valley, where it contributes to the San Joaquin River. The Merced River contains separate and unique watersheds that sustain separate hydrologic and aquatic resources and support differing levels of development. The main stem of the Merced River drains approximately 250,000 acres from the headwaters within the park to the Foresta Bridge in the El Portal Administrative Site. The main stem of the Merced River flows a total of 140 miles from its headwaters to the confluence with the San Joaquin River. Principal tributaries of the Merced River within the park boundaries include Lyell Fork, Triple Peak Fork, Red Peak Fork, Merced Peak Fork, Sunrise Creek, Illilouette Creek, Tenaya Creek, Yosemite Creek, Sentinel Creek, Ribbon Creek, Bridalveil Creek, Cascade Creek, Grouse Creek, Avalanche Creek, and Indian Creek.

The major vegetation zones of the Sierra Nevada ecosystem form readily apparent, large-scale, north-south elevational bands along the axis of the Sierra. Major east-west watersheds that dissect the Sierra into steep canyons form a secondary pattern of vegetation. On the west side, forest types change from ponderosa pine to mixed conifer to firs with increasing elevation. A subalpine and alpine vegetation zone is located on the crest of the Sierra Nevada range. Fire suppression and changing land use practices have dramatically affected natural fire regimes, altering ecological structures and functions in Sierra Nevada plant communities (UC Davis 1996a,b,c,d).

The Sierra Nevada is rich in plant diversity. As a group, Sierra Nevada plants are most at risk where habitat has been reduced or altered. However, rare local geologic formations and their derived unique soils have led to the evolution of ensembles of plant species restricted to these habitats.

About 300 terrestrial vertebrate species (including mammals, birds, reptiles, and amphibians) use the Sierra Nevada as a significant part of their range. Three modern vertebrate species once well distributed in the range are now extinct from the Sierra Nevada: Bell’s vireo, California condor, and grizzly bear. Sixty-nine species of terrestrial vertebrates (17% of Sierra Nevada fauna) are considered at risk by state or federal agencies. These species include bighorn sheep, Yosemite toad, foothill yellow-legged frog, mountain yellow-legged frog, and the western pond turtle. The most important identified cause of the decline of Sierran vertebrates has been loss of habitat, especially foothill and riparian habitats and late successional forests.

Aquatic and riparian systems are the most altered and impaired habitats of the Sierra Nevada. Dams and diversions throughout most of the Sierra Nevada have profoundly altered streamflow patterns and water temperatures. Foothill areas below about 3,300 feet appear to have the greatest loss of riparian vegetation of any region in the Sierra Nevada (UC Davis 1996a,b,c,d).

The Sierra Nevada mountain range roughly parallels the eastern boundary of California and extends from the Cascades Range in the north to the Tehachapi Mountains in the south. Cooler climates with more wind are, in general, characteristic of the mountains, as contrasted with the nearby valleys. Mountain climatic zones are characterized by considerable vertical wind motion and by winds and temperatures that differ from those in the valleys. During the warm season, wind circulation in the mountain zones is generally upslope, with only brief periods of downslope winds at night. During the cold season, wind circulation in the absence of storm activity is generally downslope, with brief periods of upslope winds on south-facing slopes.

Humans are an integral part of Sierra Nevada ecosystems, having lived and sustained themselves in the region for at least 10,000 years. Indigenous populations were widely distributed throughout the range at the time of European immigrations. Archeological evidence indicates that American Indians practiced localized harvesting, pruning, irrigation, burning, and vegetation thinning. Immigration of Euro-American settlers in the mid-1800s began a period of increasingly intense resource extraction and settlement (UC Davis 1996a,b,c,d).

As recognized in the Merced Wild and Scenic River Comprehensive Management Plan, “the scenery of Yosemite National Park is one of its most significant resources and is largely responsible for the enormous popularity of the park. Steep valley and canyon walls, clear air, spectacular rock formations, and panoramic views combine to offer a wealth of visual resources nearly unsurpassed in the United States. As people move through the varied topography and vegetation along sections of the valleys and canyons that characterize the Merced River...they experience a sequence or pattern of visual resources that in effect give a cumulative visual experience... Protecting this pattern of visual resources is as important as protecting any one visual resource” (NPS 2000c).

Recreational opportunities abound in Yosemite National Park in developed and wilderness areas alike; however, the types and quality of activities vary considerably between these two areas. Recreational opportunities are made more memorable because of the natural beauty of Yosemite Valley and wilderness environments. These areas offer a wide range of recreational experiences for the visitor, including hiking , picnicking , camping, climbing , skiing, fishing, photography, swimming , nature study, stock use , bicycling , sightseeing , and rafting . The availability of these opportunities varies by location. Most of these recreational opportunities are available in Yosemite Valley.

Park operations and facilities administered by Yosemite National Park are located within the Merced River corridor in Yosemite Valley. Park infrastructure and facilities include trails, roads, bridges and tunnels, campgrounds and lodging, and utilities. National Park Service management policies require that all facilities be managed, operated, and maintained to minimize energy consumption and development of nonrenewable fuels. The policies also require that new energy-efficient technologies be used where appropriate and cost effective.

Natural Resources

Geology , Geologic Hazards , and Soils

Regional Geology and Geologic History

Yosemite National Park occupies approximately 1,170 square miles within the central portion of the Sierra Nevada. Granitic bedrock is widespread in Yosemite National Park and dominates a significant portion of the Sierra Nevada. The granitic rock formed deep within the earth as a mass of melted rock, eventually creating subsurface bodies of solidified granitic rock called the Sierra Nevada batholith.

Between 100 million years ago and 65 million years ago, magma formation slowed and a long period of erosion began in the Sierra Nevada. Erosion  removed the overlying rocks and exposed the underlying core of the granitic batholith. About 15 million years ago, the Sierra Nevada in the Yosemite region had gently rolling upland topography and a much lower elevation than the present-day range. The Merced River flowed westward at a gentle gradient through a broad river valley. Volcanic activity, prevalent in the northern Sierra Nevada, deposited ash, filled valleys, buried streams, and altered river courses.

Later, mountain-building activity was reactivated and tilted the Sierra Nevada to form its relatively gentle western slope and the more dramatic, steep eastern slopes. The uplift increased the gradients of the rivers and resulted in deeply incised river valleys. Between 2 and 3 million years ago, snow and ice accumulated as glaciers at the higher alpine elevations and began to move westward down the mountain valleys. The downslope movement of the ice masses cut and sculpted the valleys, cirques, and other glacially formed landforms throughout the Yosemite region and the Sierra Nevada.

Project Area Geology

The Yosemite Valley segment of the Merced River contains a classic, glaciated, U‑shaped valley, providing important examples of a mature meandering river; hanging valleys such as Yosemite and Bridalveil Creeks; and evidence of glaciation (e.g., moraines below El Capitan and Bridalveil Meadows). Yosemite Valley is primarily granitic in composition and glacially carved, with its floor ranging from 3,800 to 4,200 feet above mean sea level. The Valley is oriented in an east-west direction, and its sides rise 1,500 feet to 4,000 feet above the essentially flat Valley floor. Yosemite Valley is about 6.8 miles long and varies from a little under ½ mile wide to around ¾ mile wide.

The downslope movement of the ice masses cut and sculpted the U‑shaped valley that is present today. When glaciers melt, the rock debris they transport (glacial till) is deposited in a ridge-shaped landform known as a moraine. Two prominent moraines were formed in Yosemite Valley after the last glacier retreated about 15,000 years ago. A terminal moraine, marking the furthest extent of the glacier, lies just east of Bridalveil Meadow. The El Capitan moraine, lying further east, is a recessional moraine, formed after the leading edge of the glacier had retreated up the Valley from its furthest extent. After the last glacier melted, water flow was dammed by morainal material that formed what is now referred to as the prehistoric Lake Yosemite. Stream deposits then filled in Lake Yosemite, adding to the 1,000-foot-thick sediment  that underlies the present-day floor of Yosemite Valley and covers the glacially disturbed granite rock below.

Geologic Hazards

The Merced River flows through geologically active areas, where geologic and hydrologic forces continue to shape the landform. Geologic hazards associated with these forces, such as earthquakes and rockfalls, present potentially harmful conditions to visitors, personnel, and facilities in Yosemite National Park.

The Sierra Nevada range of Yosemite National Park is not considered an area of particularly high seismic activity. Happy Isles Gauging Station Bridge lies in seismic zone 3, as defined by the Uniform Building Code Seismic Zone Map (UBC 1997). No active or potentially active earthquake faults have been identified in the mountain region of Yosemite National Park (Hart 1990); therefore, the risk of fault rupture or surface displacement beneath the bridge is negligible. Yosemite can undergo seismic shaking associated with earthquakes on fault zones to the east and west margins of the Sierra Nevada range, as has occurred in the past. These fault zones include the Foothills fault zone, the volcanically active area in the Mono Craters – Long Valley Caldera area, and along the various faults within the Owens Valley fault zone (CDMG 1996).

The Foothills fault zone extends in a north-south direction within the foothills of the Sierra Nevada, approximately 50 miles west of Yosemite Valley. This fault zone has not experienced movement in the last 2 million years and thus is not considered active or potentially active (Hart 1990). The Mono Lake fault is approximately 35 miles northeast of Yosemite Valley within the Mono Craters – Long Valley Caldera region. Over the last 12 years, this area has been one of the most seismically active regions in California. Earthquakes have been attributed to movement on the Mono Lake fault (Sierra Nevada frontal fault) and movement associated with resurgent volcanic activity of the Long Valley Caldera. The Mono craters last erupted 600 years ago. In October 1990, the Mono Lake fault experienced a 5.7 Richter movement. This earthquake was felt as far west as Sacramento and the San Francisco Bay Area and caused landslides and rockfalls at Tioga Pass and on the Big Oak Flat Road (McNutt et al. 1991).

The Owens Valley fault, located approximately 100 miles southeast of Yosemite Valley, has experienced movement within the last 200 years, and the California Division of Mines and Geology considers this fault active (Hart 1990). The most notable earthquake recorded in Yosemite National Park was the Owens Valley earthquake of March 26, 1872. The Owens Valley earthquake is estimated to have had a Richter magnitude of 7.6 and was one of the largest earthquakes in U.S. history (USGS 1991). This earthquake reportedly caused damage in Sacramento and San Joaquin Valleys and caused significant rockfalls in Yosemite Valley.

Although earthquakes that are felt by people in Yosemite National Park are relatively infrequent, they have occurred in the past and will likely occur in the future. Ground shaking can be expressed as peak acceleration due to gravity as a percent of 1 g (g is acceleration due to gravity, or 32 feet per second squared). The potential estimated peak horizontal accelerations produced by the various regional faults in the central California and Sierra Nevada region are relatively low and could range between 0 and 0.2 g (Petersen et al. 1999).[1] Most people would likely feel this range of ground shaking, but structural damage would be negligible to slight in buildings constructed according to modern building standards.

Rockfalls

Rockfall is used as a generic term to refer to all slope movement processes, including rockfall, rockslide, debris slide, debris flow, debris slump, and earth slump. Rocks have become dislodged and fallen off the sheer granite cliffs throughout the geologic history of Yosemite. Rockfalls can displace large volumes of rock and can occur due to such processes as the climate-related expansion and contraction of rock, seismic shaking, or exfoliation.

Most rockfalls are associated with triggering events such as earthquakes, rainstorms, or periods of warming that produce a rapid melting of snow. The magnitude and proximity of the earthquake, intensity and duration of the rainfall, the thickness of the snow-pack, and the pattern of warming all influence the triggering of rockfalls. However, some rockfalls occur without a direct correlation to an obvious event and are probably associated with gradual stress release and exfoliation of the granitic rocks (Wieczorek 1998).

More than 400 rockfalls have been recorded within Yosemite National Park; some have resulted in injury and, on occasion, death. Rockfalls can also damage or destroy roads, trails, and buildings. For example, Happy Isles Gauging Station Bridge was damaged by the windblast associated with the 1996 Happy Isles rockfall, when debris was blown against the bridge and damaged the metal railings (Royston et al. 1997).

Two types of areas of potential rockfall impact have been identified. The first is the area closest to the Valley or canyon walls and is called the talus zone. The second area, referred to as the rockfall shadow zone, extends out from the talus zone and is the area in which rocks may travel out from the talus. Happy Isles Gauging Station Bridge is located within the rockfall shadow zone, but is outside of the talus zone (USGS 1999b). The frequency and magnitude of rockfall events vary considerably. Many small rockfalls may occur every year and go unnoticed, while larger rockfalls occur much less frequently (Wieczorek 1998). The National Park Service, in cooperation with the U.S. Geological Survey, is currently identifying potential geologic hazards in developed areas, including areas most susceptible to rockfalls (Wieczorek 1998). The National Park Service is revising its management policies regarding geologic hazards, with the intent to better protect park visitors and staff by avoiding placement of structures in areas with a high potential for rockfall impact.

Soils

All soils form as a result of the combined effect of several factors, including composition of geologic parent material, climate, biologic activity, topographic position/relief, and time. Within the park, topography is the most important factor contributing to soil differentiation. Topography influences surface runoff, groundwater, the distribution of stony soils, and the separation of various-aged alluvial soils (NPS 1980a). More than 50 soil types are found within the park; general or local variations depend upon glacial history, microclimatic differences, and the ongoing influences of weathering and stream erosion/deposition (NPS 1978).

Soils of the Yosemite National Park region are primarily derived from underlying granitic bedrock and are of similar chemical and mineralogical composition. Various areas of Yosemite National Park have meadow soils consisting of accumulated clays, silts, and organic debris that are subjected to occasional flooding. Colluvial soils have developed along the edges of cliffs where landslides and rockslides have occurred and are composed of various-sized rocks that have high rates of infiltration and permeability. Weathering processes break down talus to smaller-sized particles that are then transported by water and eventually become deposited in alluvial fans or in stream channels (USGS 1996a).

Project Area Soils

Most of Yosemite Valley is an active floodplain of the Merced River. During Merced River flood events, alluvial soils are formed and removed as flood waters deposit and erode material over the floodplain. The active flooding builds river terraces of fine- to coarse-textured sands. Old riverbeds of boulders and gravel may be buried under the terrace soils. Residual soils are scattered throughout Yosemite Valley where bedrock weathering has occurred. Glacial soils are associated principally with moraines. Colluvial soils have developed on the talus slopes along the edges of the Valley floor. Valley soil textures vary from fine sand to fine gravel. Most soils have a generally undeveloped profile, indicating their relatively recent origin and young geologic age.

The Natural Resource Conservation Service identified 21 soil series/types in Yosemite Valley. Each soil type has specific characteristics that influence plant growth, water movement, land use capabilities, etc. Land use limitations are commonly associated with frequent flooding, seasonally high water table, poor drainage, steep slopes, high rock concentration, and a poor soil structure.

The soil profile is rather thin and poorly developed in the area surrounding Happy Isles, due to the shallow depth of underlying granitic bedrock. Soils largely consist of loam with fine sands that originate from coarse-textured stream alluvium and reworked lake sediments.

Hydrology, Floodplains, and Water Quality

The Merced River basin can be divided into three hydrologic segments: the upper Merced River, Yosemite Valley, and the Merced River gorge (which includes the El Portal Administrative Site). This division is based upon the unique watershed characteristics of the three river areas. Discharge flows within the different areas reflect the contribution of the overall watershed. The Happy Isles Gauging Station Bridge is located within Yosemite Valley.

Upper Main Stem Watershed

The upper Merced River watershed is located on the western slope of the Sierra Nevada mountains in Yosemite National Park.[2] The watershed encompasses 114,843 acres (181.9 square miles), with elevations ranging from 4,000 feet at Happy Isles Gauging Station Bridge (in Yosemite Valley at the base of the upper main stem) to over 13,000 feet at Mt. Lyell. The upper Merced descends from its headwaters through a glacially carved canyon at a gradient of about 8,000 feet over 24 miles, or an average gradient of approximately 330 feet per mile (USGS 1992). The average daily discharge rate at the upper Merced River watershed (measured at Happy Isles Gauging Station) is approximately 355 cubic feet per second (cfs), and the average annual total discharge is approximately 257,400 acre-feet (USGS 1998).

Yosemite Valley Watershed

The Yosemite Valley watershed includes Yosemite Valley and its tributary areas, as well as the Happy Isles Gauging Station Bridge project area. The main tributaries to the Merced River in Yosemite Valley are Tenaya Creek, Illilouette Creek, Yosemite Creek, and Bridalveil Creek. At Pohono Bridge, where the Yosemite Valley watershed ends and the Merced River enters the narrow, steep-sided Merced River gorge, the overall Merced River basin encompasses 205,000 acres (321 square miles) (USGS 1999a). Historic flow measurements in the river at the Pohono Bridge Gauging Station have ranged from a high of about 25,000 cfs to a low of less than 10 cfs. The mean daily discharge is about 600 cfs, with an average annual total discharge of approximately 435,000 acre-feet (NPS 1978).

During the most recent period of glaciation in Yosemite Valley, a glacier extended to approximately the location of Pohono Bridge. Following glacial retreat, a large lake (Lake Yosemite) developed and eventually filled with sediment from the El Capitan moraine to upstream of Happy Isles (Huber 1989). The resulting valley floor has a very mild slope and is responsible for the meandering pattern of the present-day river. The Yosemite Valley segment of the Merced River is characterized by a meandering river, world-renowned waterfalls, an active flood regime, oxbows, unique wetlands, and fluvial processes. The Merced River has a relatively mild slope, with an average of 0.1% through Yosemite Valley (USGS 1992). The Merced River is an alluvial river within Yosemite Valley, and the bed and banks of the channel are composed of smaller sediments, cobbles, and soil layers. This condition makes for a dynamic river that alters its course periodically by eroding and depositing bed and bank material. In most locations, the river flows through a shallow channel approximately 100 to 300 feet wide. In the middle of Yosemite Valley, the river has the capacity to convey an amount between the two- and five-year flow within the existing channel banks (NPS 1997a).

Eleven bridges cross the Merced River between Happy Isles and the Pohono Bridge. Many of these bridges influence the width, location, and velocity of the Merced River (Madej 1991). In a natural river channel, the streambanks slope at an angle away from the stream, resulting in a wider channel as flows increase. However, Yosemite bridges with arched abutments that obstruct the free flow of the Merced River—including the Happy Isles Gauging Station Bridge—confine flows in the river and result in a narrowing of the channel as flows increase. The narrowing of the channel accelerates the velocity of the river through the bridge, causing increased channel scouring directly downstream.

If flow cannot be conveyed through a bridge during periods of high discharge, water backs up behind the bridge. This backwatering can inundate low-lying areas or overflow channels. The Merced River within Yosemite Valley is constricted at all bridge sites between Happy Isles and Pohono Bridge (Milestone 1978).

Happy Isles Gauging Station Bridge

Happy Isles is located at the east Valley where the slope of the river changes from the much steeper upper main stem to the essentially flat Valley floor. At the Happy Isles Gauging Station Bridge, the river gradient is approximately 0.02 ft/ft (or 2%) (USGS 1992).[3] The gradient of the Merced River at Happy Isles Gauging Station is steeper than in the Valley floor, and the channel of the river is cut into erosion-resistant granitic boulders and talus materials, compared to channel deposits of sands and gravel present on the Valley floor. The steeper gradient and composition of streambed materials together impede meandering patterns from developing in this area.

Degradation of the riverbanks from heavy visitor use in the area surrounding the Happy Isles Gauging Station Bridge is minimized by the erosion-resistant bank materials. However, the Happy Isles Gauging Station Bridge itself has sustained quite a bit of damage in recent years. The bridge was damaged when trees hit it after the massive rockfall and windblast in the Happy Isles area in July 1996. As discussed in Chapter I, Purpose and Need, the January 1997 flood caused severe scour, undermining the full length of the river-left abutment the bridge and necessitating the bridge’s closure for public health and safety purposes. During the 1997 flood, the river rose 13.24 feet above the bed and scoured out a new thalweg beneath the bridge abutment (Eagan 1998). The abutments of the Happy Isles Gauging Station Bridge obstruct and confine the free flow of the Merced River, resulting in a narrowing of the channel by approximately 51% as flows increase (Milestone 1978). The narrowing of the channel accelerates the velocity of the river through the bridge, causing increased channel scouring directly downstream (Madej 1991). Overall, the Happy Isles Gauging Station Bridge causes the channel width of the Merced River to be reduced by half, increasing stream flow velocity and resulting in scour upstream and downstream of the bridge abutment.

Precipitation

The overall climate is temperate, with hot, dry summers and cold, wet winters. About 85% of the precipitation falls between November and April. December, January, and February have the highest average precipitation, with a monthly average of 6 inches in Yosemite Valley at 4,000 feet. Average annual precipitation in Yosemite Valley is 36.5 inches, while annual rainfall decreases to 25 inches in El Portal at 2,000 feet. Snowmelt drives the peak streamflows that occur in May and June, and minimum riverflow is observed in September and October.

Alluvial Processes

Yosemite National Park is composed of and underlain by various granite rock types; as a result, weathering, erosion, and transport of sediment can be very slow processes. Areas of Yosemite National Park have significant soil layers where clays, silts, and organic debris have accumulated with the gravels and sands of the decomposed bedrock. These soils are subject to erosion and alluvial processes.

Sedimentation is a significant process within Yosemite Valley. As noted, the Merced River has a very low gradient within the Valley, approximately 0.1%, or 6.25 feet per mile (Smillie et al. 1992). This low gradient allows for significant sediment deposition within Yosemite Valley and the formation of the meandering Merced River through this reach. River impoundments such as bridges and dams tend to alter the sediment distribution and formative streamflows, thereby disrupting the natural alluvial processes.

Floodplains

A floodplain plays a necessary role in the overall adjustment of a river system. It exerts an influence on the hydrology of the basin and also provides temporary storage for sediment eroded from the watershed. Periodic flooding provides sediment and nutrients that are essential for the aquatic and vegetative health of the floodplain. Floodplains are features that are both the products of the river environment and important functional parts of the system. However, human-made structures such as bridges and buildings placed within a floodplain can impede natural flow and result in injury to visitors and damage to structures during flood events. Discussion of flooding and floodplains is most relevant in terms of the potential loss of life and the influence on the river by development in the floodplain.

Yosemite Valley has a well-developed floodplain, with major roads and structures along or within both sides of the floodplain. The character of the floodplain varies in different locations because of local hydraulic controls. The 100-year floodplain[4] is typically used to define the general floodplain boundary. The January 1997 flood was the largest recorded within the park; it was estimated to have a recurrence interval of 90 years (NPS 1997a). The flood inundated roads, picnic areas, park offices, and lodging units. The U.S. Geological Survey estimated that the flood had a peak discharge of 10,000 cfs at Happy Isles and 25,000 cfs at Pohono Bridge (Eagan 1998).

The Merced River has a poorly developed floodplain in the area surrounding the Happy Isles Gauging Station Bridge due to the steep river gradient. The bridge adversely affects floodplains by constricting flows in the river and causing flood waters to be directed out of the channel.

Water Quality

Water quality throughout Yosemite National Park is considered to be good and generally above state and federal standards. The state of California considers the surface water quality of most park waters to be beneficial for wildlife habitat, freshwater habitat, contact and noncontact recreation, canoeing, and rafting, as indicated in the Central Valley Regional Water Quality Control Board’s Water Quality Control Plan (Basin Plan). An inventory of water quality data performed by the National Park Service indicated excellent conditions in many parts of the park, but some water quality degradation was noted in areas of high visitor use (NPS 1994b).

Occasional concentrations above drinking water and freshwater criteria have been noted within the Merced River for lead, cadmium, and mercury (NPS 1994b). Potential sources of these metals include leaded gasoline, stormwater runoff from developed surfaces such as parking lots, wastewater discharge, campsites, and fuel storage facilities.

Water quality has been affected by the extensive and concentrated visitor use of the Merced River in popular areas. High use of the streambank induces bank erosion through the loss of vegetative cover and soil compaction. Bank erosion can result in the widening of the river channel and loss of riparian and meadow floodplain areas. Water quality is then altered through increased suspended sediments due to erosion, higher water temperatures from a lack of riparian cover, and lower dissolved oxygen levels due to elevated temperatures and shallower river depths.

Human activities including the use of vehicles can distribute water pollutants that collect on land surfaces and are later transported into the river or its tributaries by stormwater runoff. Such activities are referred to as nonpoint sources because the pollutants they generate accumulate from various areas and do not originate from a single point source (such as an outfall pipe). Construction activities that disturb soil, generate dust, and cause occasional petroleum releases from equipment and vehicles can represent a short-term nonpoint pollution source. Recreational activities such as horseback riding, swimming, and hiking can lead to the introduction of organic, physical, and chemical pollutants into aquatic systems. Nonpoint-source runoff from roads and parking lots may potentially affect water quality by introducing organic chemicals and heavy metals.

Water quality at the Happy Isles Gauging Station Bridge is better than further downstream in the Valley, because nonpoint-source runoff from roads and parking lots is not present, and recreational use is less intensive. However, areas upstream of the bridge may be affected by human and animal waste and contain parasites such as giardia.

Wetlands

Regional Context

Aquatic and riparian systems are the most altered and impaired habitats of the Sierra Nevada (UC Davis 1996a,b,c,d). Dams and diversions throughout most of the range have profoundly altered streamflow patterns and water temperatures. Foothill areas below 3,300 feet appear to have the greatest loss of riparian vegetation of any region in the Sierra Nevada (UC Davis 1996a,b,c,d). Within the mountains, broad valleys with wide riparian areas were often reservoir sites, and much of the best former riparian habitat in the Sierra Nevada is now under water. The extent of the inundation across the range becomes apparent when one realizes that virtually all flatwater on the western slope of the Sierra Nevada below 5,000 feet is artificial (UC Davis 1996a,b,c,d). Wetlands in the Sierra Nevada have been drained since the earliest settlers attempted to “reclaim” meadows and other seasonally wet areas. Mountain meadows were commonly drained with the intent of improving forage conditions and to permit agriculture (Hughes 1934, as in NPS 1997c; UC Davis 1996a,b,c,d).

Wetland Classification and Definition

Wetlands are ecologically productive habitats that support a rich array of both plant and animal life. They sustain a great variety of hydrologic and ecological functions vital to ecosystem integrity. These functions include flood abatement, sediment retention, groundwater recharge, nutrient capture, and high levels of plant and animal diversity. Wetlands and riparian areas are relatively rare compared to the overall landscape. When wetlands are converted to systems that are intolerant of flooding  (drained agricultural lands, filled developed lands), their storage capacity decreases and downstream flooding increases (National Academy Press 1993, as in NPS 1997c). Modification of even small wetland areas induces effects that are proportionally greater than elsewhere in an ecosystem (Graber 1996).

Although there are several definitions for the term wetland, the two used herein follow National Park Service and U.S. Army Corps of Engineers (Corps) conventions. These definitions are presented below.

The National Park Service classifies and maps wetlands using a system created by the U.S. Fish and Wildlife Service often referred to as the Cowardin classification system (USFWS 1979). This system classifies wetlands based on vegetative lifeform, flooding regime, and substrate material. Wetlands, as defined by the U.S. Fish and Wildlife Service and adopted by the National Park Service, are lands in transition between terrestrial and aquatic systems, where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification, wetlands must have one or more of the following attributes:

·     The land supports predominantly hydrophytes, at least periodically. Hydrophytes are plants that grow in water or on a substrate that is at least periodically deficient in oxygen as a result of excessive water content.

·     The substrate is predominantly undrained hydric soils. Hydric soils are wet long enough to periodically produce anaerobic conditions.

·     The substrate is saturated with water or covered by shallow water at some time during the growing season of each year (USFWS 1979).

Under Section 404 of the Clean Water Act, the U.S. Army Corps of Engineers issues permits for the discharge of dredged or fill material into “waters of the United States” (33 Code of Federal Regulations [CFR] 323.3). Wetlands are a subset of waters of the United States and receive jurisdictional protection under Section 404 of the Clean Water Act. Waters of the United States (also regulated under Section 404 of the Clean Water Act) include features such as streams, rivers, bays, lakes, inlets, mudflats, washes, sloughs, sandflats, territorial seas, tributaries, and impoundments. Wetlands are defined under the Clean Water Act as, “Those areas that are inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions” (33 CFR 328.3[b]).

The Cowardin system and the U.S. Army Corps of Engineers both use the three wetland parameters to define wetlands: hydrophytic vegetation, hydric soil, and wetland hydrology. However, the Cowardin system defines more habitat types as wetlands than does the Corps definition. The Cowardin system also recognizes that many unvegetated sites (e.g., mudflats, stream shallows, saline lakeshores, playas, deepwater) or sites lacking soil (e.g., rocky shores, gravel beaches) are wetland habitats. The reason these sites lack hydrophytic vegetation and/or hydric soil is due to natural chemical or physical factors. Although the Corps does not consider these sites to be wetlands, they are still subject to regulations under Section 404 of the Clean Water Act as “other waters of the United States.”

The U.S. Army Corps of Engineers also has jurisdiction over navigable waters of the United States under Section 10 of the Rivers and Harbors Act of 1899. Navigable waters of the United States are those waters that are subject to the ebb and flow of the tide and/or are currently used, or have been used in the past, or may be susceptible for use to transport interstate or foreign commerce. A determination of navigability, once made, applies laterally over the entire surface of the water body and is not extinguished by later actions or events that impede or destroy navigable capacity (33 CFR 329.4). No portion of the Merced River[5] within Yosemite National Park is designated as navigable waterway under Section 10 of the Rivers and Harbors Act.

Happy Isles Gauging Station Bridge Wetlands

Using the Cowardin classification, specific wetland and deepwater classes within the project area are limited to riverine upper perennial (the main channel of the Merced River) (ESA 2001). No riparian communities (palustrine forest or palustrine scrub shrub) occur within the immediate project area (ESA 2001).

Riverine upper perennial habitat within the project area includes the open and flowing water of the Merced River that provides rich habitat for a diversity of river-related species. The habitat also includes the permanently flooded rock and cobble channel with little to no in-stream vegetation. Riparian vegetation is limited within the project area and immediately downstream by the swift flow of the Merced River and the steep banks (naturally lined with river boulders). Upstream of the bridge and outside the project area, the Happy Isles area supports palustrine forest and palustrine scrub shrub communities (riparian forest and scrub) composed of black cottonwood, white alder, black oak, and various species of willow (e.g., red willow, sandbar willow, and arroyo willow) with herbaceous species such as rush, sedge, and horsetail intermixed. The main channel of the Merced River would be subject to jurisdiction under Section 404 of the Clean Water Act by the U.S. Army Corps of Engineers as nonwetland waters of the United States.

Vegetation

The following narrative provides a general description of vegetation within the project area. Vegetation within the project area can be loosely defined as riparian and upland. Actual descriptions of vegetative communities, including distributional limits, habitat requirements, community sensitivities, and a list of plant species characteristically found in conjunction with each plant assemblage, appear in the Vegetation Management Plan (NPS 1997g).

Riparian  Plant Communities

Riparian areas and low-elevation meadows are the most productive communities in Yosemite Valley. The high quality and large extent of riparian, wetland, and other riverine areas provide rich habitat for a diversity of river-related species. Riparian vegetation is limited within the project area and immediately downstream by the swift flow of the Merced River and naturally steep and armored banks (i.e., natural river boulders). Upstream of the bridge and outside the project area, the Happy Isles area supports palustrine forest and palustrine scrub shrub communities (riparian forest and scrub) composed of black cottonwood, white alder, black oak, and various species of willow (e.g., red willow, sandbar willow, and arroyo willow) with herbaceous species such as rush, sedge, and horsetail intermixed. The riparian community upstream of the bridge is characterized by varied topography, hummocks, and depressions that create a more diverse habitat.

Upland Plant Communities

Upland vegetation in the vicinity of the Happy Isles Gauging Station Bridge is best described as a mixed conifer community composed of black oak, canyon live oak, Douglas-fir, incense-cedar, and ponderosa pine intermixed with sugar pine, manzanita, deerbrush, and bear-clover. A canyon live oak tree and several cedars are located near the Happy Isles Gauging Station Bridge. Forest density and structure within the project area have been modified by natural events (e.g., rockfall, floods) and human activity (e.g., trail use, development) in the general vicinity. The mixed conifer community is naturally adapted to frequent, low-intensity fires . Nearly 100 years of fire suppression has resulted in a change from open forest to dense thickets of shade-tolerant tree species, including incense-cedar, white fir, and Douglas-fir. However, fire does not play much of a role, if any, in this area due to the high relative humidity, presence of the river and fen, and frequent disturbance through flooding.

Wildlife

Yosemite Valley is a broad, U-shaped valley characterized by black oak woodland, lower montane mixed coniferous forest, a vigorous riparian corridor along the Merced River, low-elevation meadows, and areas of development. In Yosemite Valley, the Merced River is broad, shallow, and slow-moving (compared to other systems). The high quality and large extent of riparian, wetland, and other riverine areas provide rich habitat for a diversity of river-related species. Within Yosemite Valley, there are concentrated areas of human use that have affected wildlife and their habitats, especially in the east Valley and in the immediate vicinity of Happy Isles Gauging Station Bridge.

Mammals resident or transient in Yosemite Valley and the project area include deer mouse, California ground squirrel, western gray squirrel, broad-footed mole, Botta’s pocket gopher, ringtail, raccoon, coyote, bobcat, mule deer, mountain lion, and black bear. Heavy visitation to Yosemite Valley and its relatively high number of resident employees have led to many human/wildlife conflicts. The root of most of these problems is the availability of human food. Improperly stored food and garbage and deliberate feeding alter the natural behavior of wildlife and lead to property damage and threats to human safety. According to the park’s Black Bear Management and Incident Summary Report (on file at Yosemite National Park), over $120,000 in property damage resulted from 654 black bear incidents in the park in the year 2000.

In recent years, sightings of mountain lions in Yosemite Valley have increased. These sightings, coupled with two human fatalities in California from mountain lion attacks in 1994, have caused concern. Lions are attracted to developed areas by unnaturally high prey populations that are supported by human food sources. Further reduction of lion habitat from development or expanded human presence could impact lion populations and increase the chance of encounters.

Fisheries resources within Yosemite Valley have historically been low in species diversity. Species native to the Merced River within the Valley probably only included rainbow trout (that migrated into the area from the San Joaquin River) and the Sacramento sucker. The steep gradient and high turbulence of the Merced River gorge limited access to this reach for other species. The Sacramento sucker and rainbow trout were found only in the Valley; tributaries to higher elevations and lakes were inaccessible to even these high-gradient species.

Human activity has altered native and non-native fish populations in Yosemite Valley over the years. Non-native rainbow trout and brown trout have been stocked throughout this portion of the Merced River and currently dominate the fisheries of this area. The Sacramento sucker is still common, and an occasional brook trout is reported from the area, probably a result of transport from more favorable habitat in higher tributaries. Other species were stocked in the area, but may not have sustained populations to date. These include cutthroat trout, American grayling, and golden trout. Currently, with the exception of Sacramento suckers, which remain in all portions of the Merced River, all fishes in this portion of the Merced River are from stocked populations.

Riparian restoration  efforts are underway along the banks of the Merced River in the Valley and are likely to have a positive effect on fish populations. In 1997 and 1998, surveys were conducted to examine the effects of riverbank restoration, with special attention to the presence of large woody debris and the association of fish to those areas. Rainbow trout density appeared higher at restoration sites, while the density of browns and suckers was higher at the control sites (USFWS 1998).

Special-Status Species

The Federal Endangered Species Act of 1973, as amended, requires all federal agencies to consult with the U.S. Fish and Wildlife Service before taking actions that could jeopardize the continued existence of species that are “listed” or proposed to be listed as threatened or endangered, or could result in the destruction or adverse modification of critical or proposed critical habitat. The first step in the consultation process is to obtain a list of protected species from the U.S. Fish and Wildlife Service.

In addition, Council on Environmental Quality Regulations for Implementing the National Environmental Policy Act  (Section 1508.27) also require considering whether the action may violate federal, state, or local law or requirements imposed for the protection of the environment. For this reason, species listed under the California Endangered Species Act or accorded “special status” (i.e., considered rare or sensitive) by the California Department of Fish and Game are included in this analysis.

Also included in this analysis are park rare species. Park rare species[6] are those that have no other status (either state or federal), have extremely limited distributions in the park and may represent relict populations from past climatic or topographic conditions, may be at the extreme extent of their range in the park, or represent changes in species genetics. They are included in this analysis because they could be affected (due to proximity to human use zones, or susceptibility of individual plants or populations to loss from natural or unnatural events), and their existence is considered when evaluating consequences for any proposed management action.

The various federal, state, and National Park Service categories for special-status species are defined below:

·     Federal endangered: Any species that is in danger of extinction throughout all or a significant portion of its national range.

·     Federal threatened: Any species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its national range.

·     Federal species of concern: Any species that may become vulnerable to extinction on a national level from declining population trends, limited range, and/or continuing threats (note that this is no longer an official U.S. Fish and Wildlife Service category, but is still considered in this document because it contains many species that could become threatened or endangered).

·     California endangered: Any species that is in danger of extinction throughout all or a significant portion of its range in the state.

·     California threatened: Any species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its state range.

·     California species of special concern: Any species that may become vulnerable to extinction on a state level from declining population trends, limited range, and/or continuing threats; could become threatened or endangered.

·     California rare (plants only): A native plant that, although not currently threatened with extinction, is present in small numbers throughout its range, such that it may become endangered if its present environment worsens.

·     Park rare (plants only): Identified by the National Park Service based upon the following criteria:

–    Locally rare native

–    Listed by the California Native Plant Society

–    Endemic to the park or its local vicinity

–    At the furthest extent of its range

–    Of special importance to the park (identified in legislation or park management objectives)

–    The subject of political concern or unusual public interest

–    Vulnerable to local population declines

–    Subject to human disturbance during critical portions of its life cycle

Happy Isles Gauging Station Bridge Special-Status Species

Critical Habitat

Critical habitat has not been designated for any federally listed species that is known or has potential to occur within the project area.

Species Considered

A total of 60 special-status species (38 wildlife species and 22 plant species) have been considered in the evaluation of this project (Appendix D). Species evaluated include federally listed threatened or endangered species; species of concern (former federal category 2 species); state-listed threatened, endangered, and rare species; and species that are locally rare or threatened that are known to be or could be present within the planning area. The species list was generated based on data gathered from the National Park Service, U.S. Fish and Wildlife Service, and California Natural Diversity Database.

Special-Status Species Retained in this Analysis

Of the 60 special-status species evaluated (Appendix D), the project area supports suitable habitat for four special-status wildlife species. Table III-1 presents summary information on these species. One of these species, the bald eagle, is listed as federally threatened. Three species are listed by the federal and/or state government as species of concern (Wawona riffle beetle, harlequin duck, and California spotted owl). Each of these four special-status species is considered a river-related special-status species.

The following species accounts give a brief overview of special-status species that have potential to occur within the project area. The remaining special-status species and determination are described in Appendix D. Additional data on these species are included in the Biological Assessments for the Merced Wild and Scenic River Comprehensive Management Plan and Yosemite Valley Plan.

Federally Listed Threatened or Endangered Species

Bald Eagle. The bald eagle suffered steep population declines from the effects of pesticides in its food chain; however, bald eagle populations rebounded after DDT was banned. This resulted in the recent federal reclassification from endangered to threatened, and the bald eagle is currently being considered for delisting. The bald eagle is also state endangered.

Most bald eagles seen in the park are transients, seasonally hunting over lakes, rivers, and open terrain. Bald eagle sightings are rare in Yosemite, but most often occur in Yosemite Valley, El Portal, and Foresta. No bald eagles are known to have nested in Yosemite recently, but a pair regularly nests near the park border at Cherry Lake in Stanislaus National Forest and uses nearby Lake Eleanor inside the park for foraging.

Federal Species of Concern

Wawona Riffle Beetle. The Wawona riffle beetle is rare in rapid streams of California from 2,000 to 5,000 feet in elevation (Usingner 1956 as in NPS 2000d). The Wawona riffle beetle was previously known only from a few locations in California (Chandler 1954, as in NPS 2000d; Brown 1972 as in NPS 2000d) until more recently when it was found in several widely scattered locations in northern California, as well as southern Oregon and Idaho (Shepard and Barr 1991 as in NPS 2000d). The beetle is small, measuring less than 1 inch. Both the larvae and adult life stages are aquatic, but neither life stage actually swims. Rather, both life stages move by crawling on underwater plants and debris. Adults and larvae are found together, usually in cool, small- to medium-sized mountain streams and rivers. They are most abundant in aquatic mosses. Many taxa in this family (Elmidae-riffle beetles) are typically found clinging to stones or beneath rocks in cold, fast-running water. They are rarely found in streams with seasonal variations in flow, heavy sediments, muddy, or sandy bottoms, or low oxygen content. Suitable habitat for the Wawona riffle beetle occurs in the channel of the Merced River. The National Park Service is currently conducting surveys to determine the presence or absence of Wawona riffle beetle within the project area and throughout the Yosemite Valley segment. Survey results will be forwarded to the U.S. Fish and Wildlife Service for review and will be documented in the decision document for this project.

Harlequin Duck. Harlequin ducks are at the extreme southern extent of their range in California. They winter in marine waters along rocky coasts from San Luis Obispo County north, and breed inland along fast-flowing, shallow rivers and streams. The last known breeding of the harlequin duck in the Sierra Nevada was on the upper Mokelumne River in Amador and Calaveras Counties in the 1970s, but potential breeding habitat in California has not been adequately surveyed. Both wintering and breeding populations of the harlequin duck have declined all over California, probably due to human disturbance along breeding streams and damming of rivers.

It is likely harlequin ducks still breed in California, but rarely. Nests are established near swift rivers or streams in recesses sheltered overhead by stream banks, rocks, woody debris, or low shrubs. Nests are usually within seven feet of the water, but can be up to 90 feet away. In breeding areas, harlequin ducks feed primarily on invertebrates from the swift, shallow rivers that are its preferred habitat. In marine wintering habitat, mollusks and crustaceans are major foods. A pair of harlequin ducks was observed within the Merced River in 2000. No recent nesting harlequin ducks have been documented within Yosemite National Park. Nesting pairs of this species are presumed extirpated from Yosemite National Park.

California Spotted Owl. The California spotted owl is found from the southern Cascades south through the entire Sierra Nevada, and in the central Coast Ranges. Surveys through 1993 estimated approximately 1,600 spotted owl sites (pairs and territorial singles) in the Sierra Nevada. California spotted owl habitat varies from oak and ponderosa pine forests to lower elevation red fir forests up to 7,600 feet in elevation. Prime habitat occurs between 3,000 and 7,000 feet.

Breeding occurs from about mid-February to mid or late September, at which time the young are largely independent of their parents. Eggs are laid and incubated by the female from early April through mid May. Nests are usually tree cavities, broken-off trees and snags, abandoned nests of other species, or mistletoe clumps. Trees used for nesting are usually very large. Nesting and roosting habitat of spotted owls is typically dense forest, with a canopy closure of greater than 70%. The presence of black oak in the canopy also enhances habitat quality.

Surveys and inventories to determine the distribution and abundance of spotted owls in Yosemite were conducted in from April through August of 1988 and 1989 by the California Department of Fish and Game. Owls were seen, or responded to imitated spotted owl calls, at 58 sites over the two seasons. Two nest trees and four sites with young were observed in 1989. In Yosemite Valley, National Park Service wildlife staff has confirmed spotted owl sightings near Happy Isles, Mirror Lake, the Yosemite Chapel, and the base of Cathedral Rocks.

TABLE III-1: Special-Status Species Retained in this Analysis

Air Quality

The primary factors that determine air quality are the locations of air pollutant sources, the types and amounts of pollutants emitted, meteorological conditions, and topographic features. Atmospheric conditions such as wind speed, wind direction, and air temperature gradients interact with the physical features of the landscape to determine the movement and dispersal of air pollutants.

Climate and Meteorology

The state of California is divided into air basins that are defined partly by their meteorological and topographical characteristics. The Happy Isles Gauging Station Bridge is located in Mariposa County, which is within the Mountain Counties Air Basin.

While air quality in a given air basin is usually determined by emission sources within the basin, it also can be affected by pollutants transported from upwind air basins by prevailing winds. For instance, the California Environmental Protection Agency concluded that all of the ozone exceedances in 1995 in the southern portion of the Mountain Counties Air Basin (i.e., Tuolumne and Mariposa Counties) were caused by transport of ozone and ozone precursors from the San Joaquin Valley Air Basin (California Environmental Protection Agency 1996b). Air quality in the Mountain Counties Air Basin is also significantly affected by pollutant transport from the metropolitan Sacramento area and the San Francisco Bay Area.

Air Quality Monitoring Data

Federal, state, and local agencies operate a network of monitoring stations throughout California to provide data on ambient concentrations of air pollutants. Table III-2 summarizes recent monitoring data from monitoring stations in the project vicinity. Three of the stations that contributed to table III-2 are located in Yosemite National Park (Turtleback Dome, Wawona, and Yosemite Valley Visitor Center) and one is located outside of the park in the Sierra National Forest (Jerseydale). Wawona, Yosemite Valley Visitor Center (in Yosemite Village), and Jerseydale are approximately 4,000 feet above sea level, and Turtleback Dome is approximately 5,300 feet above sea level. As shown in table III-2, exceedances of state and national standards for ozone and state standards for PM-10 are recorded on occasion within the park and in the park vicinity.

Ozone

Ozone is a reactive pollutant that is not emitted directly into the atmosphere, but is a secondary air pollutant produced in the atmosphere through a complex series of photochemical reactions involving volatile organic compounds (VOC) and oxides of nitrogen (NOx). VOC and NOx are known as precursor compounds for ozone. Significant ozone production generally requires ozone precursors to be present in a stable atmosphere with strong sunlight for approximately three hours. Ozone is a regional air pollutant because it is not emitted directly by sources, but is formed downwind of sources of VOC and NOx under the influence of wind and sunlight. Short-

TABLE III-2: Recent Ozone and PM-10 Concentration Data for Yosemite National Park and Vicinity

Pollutant	National Standard	State Standard	Monitoring Data By Year
			1995	1996	1997	1998	1999
Ozone Monitoring Data Station: Yosemite National Park - Turtleback Dome
Highest 1-hr. average, ppma	0.12	0.09	0.11	0.11	0.11	0.11	0.10
Number of state exceedancesb			11	9	3	10	4
Number of national exceedances			0	0	0	0	0
Highest 8-hour average, ppm	0.08	NA	0.10	0.09	0.10	0.10	0.09
Number of national exceedances			11	10	3	9	4
Station: Yosemite National Park – Wawona
Highest 1-hour average, ppma	0.12	0.09	0.11	0.10	ND	ND	ND
Number of state exceedancesb			9	8
Number of national exceedances			0	0
Highest 8-hour average, ppm	0.08	NA	0.09	0.09	ND	ND	ND
Number of national exceedances			2	1
Station: Sierra National Forest - Jerseydale (approximately 12 miles west of Wawona)
Highest 1-hr. average, ppma	0.12	0.09	0.11	0.11	0.12	0.11	0.16
Number of state exceedancesb			16	26	7	12	13
Number of national exceedances			0	0	0	0	1
Highest 8-hour average, ppm	0.08	NA	0.10	0.11	0.11	0.10	0.11
Number of national exceedances			22	30	7	14	21
Particulate Matter (PM-10) Monitoring Data Station: Yosemite Village – Visitor Center
Highest 24-hr. average, mg/m3 a	150	50	71	106	62	40	82
State Exceedances/Samplesc			5/56	4/46	1/56	0/55	2/55
National Exceedances/Samples			0/56	0/46	0/56	0/55	0/55
Annual Geometric Mean, mg/m3	50	30	24.2	20.3	19.6	18.0	ND

a  ppm = parts per million; mg/m3 = micrograms per cubic meter.

b  For ozone, “number of exceedances” refers to the number of days in a given year during which the standard was exceeded.

c   PM-10 is usually measured every sixth day (rather than continuously like other pollutants). For PM-10, “exceedances/samples” indicates the number of exceedances of the standard that occurred in a given year and the total number of samples that were taken that year.

Note: NA = Not applicable. ND = No data available. Values shown in bold type exceed the applicable standard.

Source:            California Environmental Protection Agency, Air Resources Board, California Air Quality Data, 1995, 1996, 1997; California Ambient Air Quality Data 1980-1999, Data CD, November 2000b.

 

term exposure to ozone can irritate the eyes and cause constriction of the airways. Besides causing shortness of breath, ozone can aggravate respiratory diseases such as asthma, bronchitis, and emphysema.

Table III-2 shows that exceedances of state (1-hour) and national (8‑hour) ozone standards occurred on an average of 2 to 19 days per year in the past five years for which data are available. The data suggest that ozone exceedances occur more frequently in Sierra National Forest than in Yosemite National Park, and that exceedances in the park are more frequent in Yosemite Valley closer to the project site than in Wawona. Exceedances of the ozone standards are a summertime phenomenon, with most of the exceedances in July, August, and September and only occasional exceedances in June and October. As discussed previously, ozone concentrations in Yosemite National Park are largely a function of pollutant transport from San Joaquin Valley, Sacramento, and, to a lesser extent, the San Francisco Bay Area. The principal sources of ozone precursor emissions in San Joaquin Valley include on-road motor vehicles, oil and gas production, farming operations, and pesticide use. On-road motor vehicles account for approximately 33% and 46% of VOC and NOx, respectively, in San Joaquin Valley (California Environmental Protection Agency 1998). Emissions of ozone precursor emissions are expected to decrease approximately 15% between 1996 and 2010, based on the most recent emissions inventories and forecasts published by the Air Resources Board. This forecast decrease in ozone precursors largely reflects the continuing beneficial effect from state and federal motor vehicle emissions control standards and programs. Within the park, emissions of ozone precursors are generated by such sources as motor vehicle traffic, and gasoline and diesel-powered equipment.

Particulate Matter (PM-10 and PM-2.5)

PM-10 consists of particulate matter that is 10 microns or less in diameter (a micron is one 1‑millionth of a meter), and PM-2.5 consists of particulate matter 2.5 microns or less in diameter. Both PM-10 and PM-2.5 represent fractions of particulate matter, which can be inhaled into the air passages and the lungs and can cause adverse health effects. Particulate matter in the atmosphere results from many kinds of dust- and fume-producing industrial and agricultural operations, combustion, and atmospheric photochemical reactions. Some of these operations, such as demolition and construction activities, contribute to increases in local PM-10 and PM-2.5 concentrations, while others, such as vehicular traffic, affect regional PM-10 and PM-2.5 concentrations.

Table III-2 shows that exceedances of the state 24-hour-average PM‑10 standard occur approximately 5% of the time in Yosemite Village. No exceedances of the less stringent national standard of 150 micrograms per cubic meter have been recorded over the past five years. PM-2.5 monitoring capability is expected to be added to the monitoring station in Yosemite Village in the near future. Under some conditions, concentrations of PM-10/PM-2.5 in the park largely reflect pollutant transport from upwind areas, such as the San Joaquin Valley Air Basin, while under other conditions, ambient concentrations reflect local sources such as campfires, entrainment of dust from vehicle movement over paved roads (particularly from wintertime sanding of roads for traction), and prescribed fires. Regional emissions of PM-10/PM-2.5 and their precursors (VOC, NOx, and sulfur dioxide) within San Joaquin Valley are expected to decrease over the next decade or so, primarily due to reductions in emissions anticipated to result from state and federal motor vehicle emissions control standards and programs. Local emissions of PM‑10/PM-2.5 would continue to be proportional to the number of campsites, the extent of vehicular travel on park roads, and frequency and extent of prescribed fires.

Sensitive Receptors

Land uses such as schools, child care centers, hospitals, and convalescent homes are considered to be more sensitive than the general public to poor air quality because the population groups associated with these uses have increased susceptibility to respiratory distress. Persons engaged in strenuous work or exercise also have increased sensitivity to poor air quality. Residential areas are considered more sensitive to air quality conditions than commercial and industrial areas because people generally spend longer periods of time at their residences. Recreational uses are also considered sensitive compared to commercial and industrial areas due to the greater exposure to ambient air associated with outdoor activities.

Trail and recreational users along the Merced River, including those visiting the Nature Center at Happy Isles, would be the closest sensitive receptors to project construction. Sensitive land uses located slightly further from the site include the Lower and Upper Pines Campgrounds and Curry Village, which are just over a quarter-mile northwest of the project site.

Noise

Introduction

By definition, noise is human-caused sound that is considered to be unpleasant and unwanted. Whether a sound is considered unpleasant depends on the individual listening to the sound and what the individual is doing when the sound is heard (e.g., working, playing, resting, sleeping). While performing certain tasks, people expect and, as such, accept certain sounds. For instance, if a person works in an office, sounds from printers, copiers, and keyboards are generally acceptable and not considered unpleasant or unwanted. By comparison, when resting or relaxing, these same sounds are not desired. The desired sounds during these times are referred to as natural quiet, a term used to describe ambient (outdoor) natural sounds without intrusion of human-caused sounds. Natural quiet can be essential in order for some individuals to achieve a feeling of peace and solitude.

Natural sounds within Yosemite National Park and adjacent to the Merced River are not considered to be noise. These sounds result from natural sources such as waterfalls, flowing water, animals, and rustling tree leaves. The enjoyment of natural sounds along the river contributes to the Yosemite visitor’s experience. Noise within the park results from mechanical sources such as motor vehicles, generators, and aircraft, and from human activities such as talking and shouting.

Sensitive Receptors

Some land uses are considered more sensitive to ambient noise levels than others, due to the amount of noise exposure (in terms of both exposure duration and insulation from noise) and the types of activities typically involved. Residences, motels and hotels, schools, libraries, churches, hospitals, and parks and other outdoor recreation areas are generally more sensitive to noise than commercial and industrial land uses.

Trail and recreational users along the Merced River, including those visiting the Nature Center at Happy Isles, would be the closest sensitive receptors to project construction. Sensitive land uses located slightly further from the site include the Lower and Upper Pines Campgrounds and Curry Village, which are just over a quarter-mile northwest of the project site.

Existing Noise Sources

Motor Vehicles

The noise environment at the project site is primarily influenced by people using the trails and nearby facilities. The noise environment closer to the Upper and Lower Pines Campgrounds and Curry Village is influenced by automobiles, shuttle buses, recreational vehicles (including noise from generators), and trucks and by camper conversations and activities. Noise from motor vehicles is obviously loudest immediately adjacent to campground and other park roadways but, due to generally low background sound levels, can be audible a long distance from the road. Atmospheric effects such as wind, temperature, humidity, topography, rain, fog, and snow can significantly affect the presence or absence of motor vehicle noise near the project site. Logically, noise levels from this source will be loudest where and when activity levels are the greatest and nearest to the area.

Aircraft

As part of a report to Congress (NPS 1994a), the National Park Service conducted a visitor survey in Yosemite National Park. Of the visitors surveyed, 55% reported hearing aircraft sometime during their visit. The report notes that recognition of noise from aircraft was highly variable from location to location and, logically, that impacts were greater for activities when respondents had removed themselves from automobiles and from crowded visitor areas. In Yosemite, a majority of the complaints came from wilderness trail users. Measurements made in 1993 at four locations within the park (Rafferty Creek, the Soda Springs area in Tuolumne Meadows, Mirror Lake, and Glacier Point) indicated that aircraft were audible 30% to 60% of the time during each of the measurement periods (six hours at each site). Most overflights are associated with high-altitude jet aircraft. The National Park Service also uses aircraft in its management activities. These aircraft are generally helicopters used for firefighting, search and rescue, medical, law enforcement, and other special operations (NPS 1993b).

Other Sources

Other mechanical sources of noise within the park and near the Merced River include road construction equipment, generators, radios, and park maintenance equipment (i.e., mowers and chainsaws). The frequency of use and the location of these sources vary both by season and reason for use.

Background Sound/Noise Levels

Current background sound levels adjacent to the main stem of the Merced River vary by location and also by season (the volume of water in the river being lower in the fall and higher in the spring). Current background noise levels are influenced by the number of visitors to the park and by the proximity of mechanical noise sources.

Sound and noise levels are measured in units known as decibels (dB). For the purpose of this analysis, sound and noise levels are expressed in dB on the “A”-weighted scale (dBA). This scale most closely approximates the response characteristics of the human ear to low-level sound. Human hearing ranges from the threshold of hearing (0 dBA) to the threshold of pain (140 dBA). Environmental sound or noise levels typically fluctuate over time, and different types of noise descriptors are used to account for this variability. One of these descriptors is the energy-equivalent level (Leq), which is the equivalent steady-state level which, in a stated period, reflects the same acoustic energy as the actual time-varying level during the same period.

As part of the Merced Wild and Scenic River Comprehensive Management Plan, sound-level measurements were obtained at various locations adjacent to the Merced River (from the headwaters of the Merced River to the base of Vernal Fall). Measurements were obtained with a Larson Davis dosimeter (Model 700). The dosimeter was calibrated with a Larson Davis sound-level calibrator. At each measurement location, observations of the background level were made over a period ranging from one to five minutes. In addition, observers noted the sources contributing to the background level and noted any sources that caused intrusive levels above the typical background level.

Several measurements were taken in the vicinity of the Happy Isles Gauging Station Bridge. A noise level of 59 Leq was measured in the Happy Isles area on a Saturday in September 1999 at 2:40 p.m. Most of the noise came from people using the trails and facilities nearby. Another set of measurements was taken at a point in the Upper Pines Campground midway between the Merced River and the main access road to the campground. A noise level of 55 Leq was measured at 5:45 p.m. on that same day at this location; a second measurement the next morning at 6:00 a.m. yielded a noise level of 32 Leq when no human-caused noise was discernible.

Regulatory Standards

Generally, the federal government sets standards for transportation-related noise sources that are closely linked to interstate commerce, such as aircraft, locomotives, and trucks; for those noise sources, state governments are preempted from establishing more stringent standards. The state governments set noise standards for transportation-related noise sources that are not preempted from regulation, such as automobiles, light trucks, and motorcycles. Noise sources associated with industrial, commercial, and construction activities are generally subject to local control through noise-related plans and policies.

Cultural Resources

Introduction

The Happy Isles Gauging Station Bridge (also known as the Old Happy Isles Bridge and Happy Isles footbridge), which spans the Merced Wild and Scenic River, is a reinforced-concrete girder bridge supported on concrete masonry abutments. It was originally constructed in 1921, but has been substantially altered since that time. The Happy Isles Gauging Station and streamflow gauge, adjacent to the river-right abutment of the bridge, is one of 49 benchmark gauges located in the United States. The gauge was selected as a natural hydrologic benchmark because of its location within a national park on a stream largely unaffected by human activity. In 1915, a staff gauge was bolted to a large boulder on the downstream side of the river-right bank pier at Happy Isles.  Replaced in 1916 by a water-stage recorder, the existing gauge provides the longest continuous record of streamflow data available in California, and acts as an early warning system for floods in Yosemite Valley. Happy Isles Gauging Station is considered a historic resource that is eligible for the National Register of Historic Places and is a contributing feature to the Yosemite Valley Cultural Landscape. In 1975 the original rustic gauge housing was destroyed and replaced with the current wooden housing. The stone footing and gauge location have remain unaltered since construction in 1916.

In 1994, as part of the Section 106 documentation of the Yosemite Valley Cultural Landscape, the Happy Isles Gauging Station Bridge was listed as a contributing resource related to Yosemite Valley’s circulation system. The Section 106 documentation also noted that the Yosemite National Park Roads and Bridges Recording Project included written historical and descriptive data, measured drawings, and Historic American Engineering Record photographs for the “Old Happy Isles Bridge.”

The Happy Isles Gauging Station Bridge was severely damaged during the flood of January 1997 and was deemed unsafe by representatives of the Federal Highway Administration. The National Park Service closed the bridge for safety reasons in July 1997.

Overview of Human Occupation

American Indians

Yosemite Valley includes evidence of thousands of years of human occupation, reflected in the large number of archeological sites. The National Park Service presently has evidence for the habitation by American Indians in the Yosemite area between 4,000 and 6,000 years ago. Some preliminary evidence from the El Portal area indicates people may have been living there as long as 9,500 years ago. The park area contains hundreds of archeological sites, evincing thousands of years of occupation. There is evidence of technological change through time, a highly developed trade network, at least one population replacement, and significant environmental manipulation through the use of fire.

When Euro-Americans first entered Yosemite Valley in 1851, the American Indians living there were primarily Southern Sierra Miwok with individuals joining or visiting them from the Mono Lake Paiute and Central Sierra Miwok band and even some individuals from the disbanded missions (post 1820s). The upland areas of the Merced River drainage were frequented by Southern Sierra Miwok, and the Mono Lake Paiute, and at least traversed by Western Monos and possibly Chukchansi Yokuts.

The Mariposa Indian War of 1851 was triggered by the influx of Euro-American miners, ranchers, farmers, and merchants taking American Indian lands since 1848. After 1851, as awareness of Yosemite Valley grew, hotels and other travel-related amenities were developed. Due to the growth of hotels and tourist-related activities, additional Mono Lake Paiutes arrived and remained in Yosemite Valley as part of the workforce. The Indian Treaties of 1851 were never ratified by the U.S. Senate and management of the Valley was taken over by Euro-American institutions, and American Indian interests were subject to decisions made without their influence. Traditions changed as Indian people built nontraditional houses, vacated old village sites, and built new villages. These changes were due in part to efforts by Euro-Americans to centralize the Indian people as a tourist “attraction” and control their activities.

Indian people continue to live in and around the park, and many are employed by the National Park Service, the concessioner, or other local businesses. At least seven Indian tribes claim traditional associations with Yosemite National Park, and the National Park Service has entered into various agreements with the American Indian Council of Mariposa County, Inc., the political organization representing the Southern Sierra Miwok tribe. Individuals from most of these tribes continue to maintain cultural associations with lands and resources in Yosemite National Park through traditional ceremonies, gathering of traditional plants, and other activities.

Euro-Americans

The first Euro-Americans to enter the Yosemite region was a party of hunters and trappers, led by Joseph R. Walker, who made an east-west crossing of the Sierra Nevada in October of 1833. Probably following a portion of the old Mono Indian Trail, along the crest between the Merced and Tuolumne Rivers, the expedition passed through what is now Yosemite National Park. It is not known whether the party viewed the Yosemite Valley.

In October of 1849, William Penn Abrams, while tracking a grizzly bear from Savage’s Trading Post (at the junction of the Merced River and the South Fork approximately 10 miles from the park’s west boundary) described his first view of what was unquestionably the Yosemite Valley. Although Abrams made no mention of American Indians, Chief Tenaya and his people were residing in the region at the time.

With the advent of the Gold Rush, parties of miners began traversing every river, stream, and drainage in the Sierra Nevada foothills, and many made their way up the Merced River to the Yosemite Valley, where they encountered American Indians in their villages. The expedition of the Mariposa Battalions of 1850 and 1851, intended to exterminate the American Indians, was touted as the first expedition into the Valley. Two years later Lt. Tredwell Moore, on a punitive expedition against Chief Tenaya and his band of Yosemite Miwok, made the first documented visit to Yosemite over the Mono Trail.

Although Indian trails had existed in Yosemite for thousands of years, the impetus to build roads in the area came largely from the development of tourism, which began in 1855 when J.M. Hutchings led the first tourists into the Valley. An improved trail to the Valley was constructed in 1856, from Mariposa by way of the South Fork of the Merced River. By 1856, regular tourist travel had been established, and the first Valley floor hotel (the Lower Hotel) was built that same year.

Transportation

Numerous other trails were established to bring tourists into the Valley. One of the earliest routes, established in 1856, was the Mann Brothers (Mariposa) Trail through Clark’s Station (Wawona) and Inspiration Point. The Coulterville Free Trail, also built in 1856, traveled from Bull Creek through Deer Flat, Hazel Green, Crane Flat, and Gentry’s to the Valley.

The first roads into the Valley were completed almost simultaneously: the Big Oak Flat Road in 1871, the Mariposa (Wawona) Road in 1874, and the Coulterville Road that same year. All the early roads into Yosemite were privately owned toll roads. In 1907, the Yosemite Valley Railroad was completed from Merced to its terminus at El Portal, and passengers could travel a wagon route to the floor of the Valley. After the development of roads into the Valley, trails, bridges, and interconnecting roads soon followed. By the 1880s, a network of routes between lodging and scenic locations had been established.

At the urging of John Muir, and with continuing pressure from motorist groups, the state of California declared the construction of the “All Year Highway” from Mariposa through El Portal to the Valley to be its top priority. The road (El Portal Road) was completed in 1926, with a new entrance station located at Arch Rock near the park’s western boundary.

The 1920s was also a decade of intensive trail and bridge building in Yosemite Valley. The Valley Loop Trail, designed in the late 1920s, necessitated the construction of 14 bridges. This trail, in basically the same location, was depicted on historic maps of the Valley in the early 1900s.

During the late 1920s, due to lack of funds and as a matter of general policy, the National Park Service did not build separate trails for hikers and equestrians. Therefore, the trails and bridges were designed for both pedestrian and stock use. The bridges built in the late 1920s, like the trails, were designed to be “in harmony with nature,” as the first National Park Service Director Stephen Mather had decreed.

Tourism

Inspired by artists and writers who portrayed the magnificence of Yosemite’s wonders, tourists began to pour into Yosemite Valley in large numbers. Numerous tourist-related businesses were established, primarily in the area of the Old Village, on the south bank of the Merced River.

Settlement and Agriculture

Lafayette Bunnell and his companions constructed the first non-American Indian structure on the Valley floor in 1855, a rough structure of canvas and wood. The Lower Hotel was completed in 1856, and meadows were planted with hay and grain to support livestock. The Upper Hotel was completed the following year. James Lamon built a log cabin in 1859, with other cabins, outbuildings, orchards, and vegetable gardens soon thereafter.

In 1864, J.M. Hutchings, significant in the history of Yosemite as a guide, hotel keeper, and publisher of Hutchings California Magazine, took over Hite’s House (Upper Hotel) at the site of the Old Village. The following year he built a new winter home on the north side of the Valley, where he resided until his death in 1902.

Other hostelries, camps, hotels, and lodging facilities were constructed, burned, torn down, removed, and rebuilt over the following years. But Hutchings’ establishment and his writings did more to popularize Yosemite than the works of any other person, with the exception of John Muir. Ironically, Muir obtained his first employment in the Valley at Hutchings’ sawmill, where he built a cabin in the meadow behind Hutchings’ home.

Yosemite National Park

Congress established Yosemite as a preserve in 1864, when the Yosemite Valley and Mariposa Big Trees, containing 60.4 square miles, were granted to California as public trust on June 30. Even though it was not considered a “national park” at the time, it is clear from the legislation that the intent was to preserve a national treasure. A much larger protected area was created around the original 36,111 acre Yosemite Valley Grant in 1890, when surrounding reserved forest lands were added. The area that became Yosemite National Park was created on October 1, 1890 totaling 932,000 acres. It included the Minarets, Devils Postpile, and the high elevation country of the Merced and Tuolumne Rivers headwaters.

However, the state could not afford to provide the financial backing required to maintain the park. Soon after the turn of the nineteenth century, the deterioration of the Valley under the state’s management led to a movement, primarily by John Muir, Theodore Roosevelt, and Governor George C. Pardee, to return the Yosemite Grant to the federal government to be part of the national park. As a result, several bills were introduced into the legislature for re-cession of the Yosemite Grant. The act was signed into law on March 3, 1905 and on June 6, 1906, the acting superintendent was directed to move his headquarters to Yosemite Valley and take charge of the Valley and Big Tree Grove. In 1916 the National Park Service Act was passed and Stephen T. Mather was made the first director of Yosemite National Park. Over the ensuing years, numerous boundary changes, primarily on the western edge, have restructured the park, which now totals 1,170 square miles.

Archeological Resources

To date, approximately 6% of Yosemite National Park has been inventoried for archeological resources, and over 1,100 archeological sites have been documented. Most of the inventories focus on lower elevation developed areas and road corridors; however, some wilderness areas have been surveyed. In most cases, inventories have been conducted in support of park development projects as part of the environmental and historic preservation compliance process. The most recent comprehensive overview of archeological resources and their information value is presented in An Archeological Synthesis and Research Design for Yosemite National Park, California (Hull et al. 1999). This document summarizes the results of past archeological research and presents research questions and methodologies for improving understanding of prehistoric and historic lifeways in the Yosemite region.

In general, archeological sites are important for the information they can provide regarding prehistoric and historic lifeways. Prehistoric and historic American Indian sites are important to Indian people as a tangible link with the past. Prehistoric sites in Yosemite generally contain some of the following: flaked and ground stone tools, waste from tool manufacturing, food processing features, fire hearths, structural remains, human burials, and rock art. Historic archeological sites provide important information not available in written records, such as construction techniques, lifestyle of early settlers, trade and procurement of goods and materials, and interactions with native peoples. Historic sites include structural remains, waste dumps, work camps, and remains of industrial activities such as logging and mining.

Archeological resources in the Happy Isles area include historic and prehistoric sites. The historic sites are associated with development and use of the area as a travel corridor and location of a power plant, streamflow gauging station, fish hatchery, and nature center. No prehistoric resources have been identified within the project boundaries, although several sites have been recorded nearby. As the area is tumbled by stream activity every spring, and as rockslides are prevalent, it is unlikely that this area would have been an occupation site. The ground and trails near the Nature Center at Happy Isles and snack stand have been compacted with dirt and asphalt for years, and as a result, identification of any prehistoric activity is unlikely.

Ethnographic Resources

Indian people continue their traditional cultural associations with parklands and resources. While little formal research has been conducted to inventory and document traditional resources important to Indian people, Yosemite Valley has been the focus of such a study. Cultural association studies are currently underway for both the northern and southern portions of the park. Information about places and traditional uses should be forthcoming from these studies. A parkwide ethnographic overview was prepared during the 1970s, but needs to be revised based on currently available information. Some ethnohistory studies, mostly focusing on Yosemite Valley and El Portal, have also been conducted.

The National Park Service consults with American Indian people about management of parklands, especially regarding undertakings and park resources of concern. Some of the primary concerns are access to park areas; gathering of plant materials for food, medicinal, and utilitarian purposes; protection of archeological and burial sites; and interpretation of Indian culture and prehistoric and historic lifeways. The National Park Service is required to consult on the basis of Government-to-Government Relations with federally recognized Indian tribes, and on a more informal basis with nonfederally recognized tribes. The National Park Service has entered into an agreement with the American Indian Council of Mariposa County, Inc., for purposes of traditional practices and the establishment of an Indian Cultural Center at the site of the last historic Indian village in Yosemite Valley, west of Camp 4 (Sunnyside) Campground. The National Park Service is working with park associated American Indian groups to develop a plan consistent with the Native American Graves Protection and Repatriation Act (NAGPRA) to deal with inadvertent discoveries of human remains and funerary objects.

There is no ethnographic information or direct historical data related to American Indian occupation or current enthnographic use in the immediate project area. There is a historic village site north of Happy Isles, and information on the use of Happy Isles as a historic travel and trade corridor and a gathering area for plant resources.

The Southern Sierra Miwok and possibly the Mono Lake Paiute are associated with lands and resources along the Merced River.

Cultural Landscape Resources, including Historic Sites and Structures

Comprehensive inventories and evaluations of historic sites, structures, and cultural landscape resources have been undertaken for Yosemite Valley. According to the DO-28 Cultural Resources Management Guidelines (NPS 1991b), a cultural landscape is:

      …A reflection of human adaptation and use of natural resources and is often expressed in the way land is organized and divided, patterns of settlement, land use, systems of circulation, and the types of structures that are built. The character of a cultural landscape is defined both by physical materials, such as roads, buildings, walls, and vegetation, and by use reflecting cultural values and traditions.

Thus, cultural landscapes are the result of the long interaction between people and the land, and the influence of human beliefs and actions over time upon the natural landscape. Shaped through time by historical land use and management practices as well as politics, property laws, technology, and economic conditions, cultural landscapes provide a living record of an area’s past, a visual chronicle of its history. The dynamic nature of modern human life contributes to the continual reshaping of cultural landscapes, making them a good source of information about specific times and places, but at the same time rendering their long-term preservation a challenge. Nationally significant historic resources are found within the Yosemite Valley segment of the Merced River, such as designed landscapes and developed areas, historic buildings, and circulation systems (trails, roads, and bridges) that provide visitor access to the sublime views of natural features that are culturally valuable.

The crossing of the Merced River at Happy Isles has a long history that began with Indian trails into the region that were later improved for tourist travel. The term “Happy Isles” was bestowed upon the three islets in the 1880s. As early as 1883, the “Tis-sa-ack Bridge” was located on the same site and carried travelers on the “Tis-sa-ack Avenue Road” across the Merced River. “Tis‑sa-ack” was the early settlers’ understanding of the Yosemite Indians name for Half Dome (NPS 1999b).

The Tis-sa-ack Bridge was renamed the “Power House Bridge” by 1909 (it was named after the electrical plant built on one of the islets in 1902). At that time, it was an 86-foot-long wooden structure. In addition to the powerhouse, several employee residences (no longer extant) were located near the bridge. In 1920, Park Superintendent Lewis referred to the bridge as “prehistoric” and in a “very marked state of decay.” Funds were appropriated for its replacement, and in 1921 the bridge was replaced with the present reinforced-concrete girder structure (NPS 1999b). The bridge was designed by the National Park Service engineering office in Portland, Oregon.

The new bridge served as a vehicle bridge for a very short time. In 1929, during the era of intense bridge building in the park, a stone-faced concrete bridge was erected some 500 feet downstream. Now called the Happy Isles Vehicle Bridge, vehicle traffic was routed over its span, with the old bridge relegated to accommodating pedestrian traffic and pack animals (NPS 1999b). The old bridge, however, is a locally rare example of a concrete girder bridge in Yosemite National Park, the prevailing form of construction in the late 1910s and 1920s.

The bridge has also been substantially altered. The original concrete window pane balustrade has been replaced with a railing of heavy steel pipes supported by steel I-beams, while older parts of the concrete have been sprayed with gunite or stucco (NPS 1999b).

The Happy Isles Gauging Station and streamflow gauge, another important historic resource, is adjacent to the bridge and protected by its river-right abutment. In August 1915, a staff gauge was bolted to a large boulder on the downstream side of the river-right bank pier at Happy Isles to measure water flow. The original gauge at Happy Isles was replaced in November 1916 by an automatic water-stage recorder, housed in a 14-foot-square enclosure supported by log pillars and topped by a hipped roof. The station began recording in September 1918. Two other gauging stations were established on the Merced River: one at the confluence of the Merced River and Illilouette Creek and one above Illilouette Creek. The original Happy Isles Gauging Station housing was smashed by a fallen tree in April 1975 and replaced by the present, less distinctive gabled structure (NPS 1999b).

Also located nearby was a state fish hatchery, built in 1927. The hatchery was closed in 1956, and the building converted and developed as the Nature Center at Happy Isles the following year.

Existing Environmental and Associated Cultural Resource Documentation

The Happy Isles Gauging Station Bridge has been the subject of previous evaluation and mitigation actions. Based on a cultural resources inventory of Yosemite National Park completed in 1994, the Happy Isles Gauging Station Bridge is a contributing feature of the Yosemite Valley cultural landscape, eligible for listing in the National Register of Historic Places. In 1991 the bridge was documented to Historic American Engineering Record standards, which included historical and descriptive data, measured drawings, and archival photographs. In accordance with the protocols agreed upon by Yosemite National Park and the State Historic Preservation Officer on March 20, 1997, the current level of documentation for the Happy Isles Gauging Station Bridge was determined sufficient.

In addition to compliance with the stipulations of the 1997 agreement, removal of the bridge would comply with the requirements of the Yosemite Valley Plan. These requirements are included in the 1999 Programmatic Agreement between the National Park Service, the State Historic Preservation Officer, and the Advisory Council on Historic Preservation for the “Resolution of Adverse Effects” associated with planning, construction, operations, and maintenance activities within Yosemite. One stipulation for removal of the Happy Isles Gauging Station Bridge remains: formal consultation with the State Historic Preservation Officer for this adverse action to a National Register eligible structure. This stipulation, to coordinate Section 106 (Section 36 CFR Part 800) consultation with the State Historic Preservation Officer and the Advisory Council on Historic Preservation, is required under the National Historic Preservation Act of 1966. Consensus will be requested from the agencies upon completion of the environmental assessment.

Social Resources

Scenic Resources

The Happy Isles Gauging Station Bridge is located in east Yosemite Valley, an area well-known for its remarkable scenic vistas. Dramatic rock walls rise above the Merced River in the vicinity of Happy Isles, including the western flank of the rock mass that includes Mt. Broderick and Half Dome, the base of which is approximately 200 feet beyond the river-right bank; the wall rising to Glacier Point, approximately 800 feet west of the river-left bank; and North Dome and Washington Column, directly downstream, approximately 1.5 miles from the Happy Isles Gauging Station Bridge.

In terms of landscape features most visitors look for and are able to distinguish, Glacier Point, North Dome, and Washington Column are 3 of the 11 most important features within Yosemite Valley, as identified in a visual analysis conducted by the National Park Service in the late 1970s. The visual analysis evaluated all points from which the 11 features could be seen to establish the scenic viewing potential of different locations on the Valley floor. The visual analysis also identified areas within the Valley that were consistently selected by eminent historic photographers and painters as the best areas for photographing and painting scenic features. Based on this analysis, locations in the Valley were classified as A-Scenic (viewpoints most commonly selected by eminent photographers and painters), B-Scenic (points less commonly selected), or C-Scenic (areas of minor scenic quality). The reach of the river that includes the Happy Isles Gauging Station Bridge is identified as B-Scenic, as shown on the Yosemite Valley Scenic Analysis map based on the National Park Service study (NPS 2000c). The B-Scenic classification indicates that the Happy Isles area is “included in scenic views less commonly chosen by historic photographers and painters, or compose[s] less significant modern views, based on park management observations” (NPS 2000c).

The Merced River itself at Happy Isles contributes substantially to the area’s scenic value. Its banks are lined with boulders and trees and other vegetation. In spring the river changes from calm, clear, and green to white and frothy, as series of riffles interrupt more placid sections both upstream and downstream of the Happy Isles Gauging Station Bridge. Immediately upstream of the bridge, the river encircles the small islands for which this area was named.

As identified in the Merced Wild and Scenic River Comprehensive Management Plan, Yosemite Valley provides magnificent views from the river and its banks of waterfalls (Nevada, Vernal, Illilouette, Yosemite, Sentinel, Ribbon, Bridalveil, and Silver Strand), rock cliffs (Half Dome, North Dome/Washington Column, Glacier Point, Yosemite Point/Lost Arrow Spire, Sentinel Rock, Three Brothers, Cathedral Rock, and El Capitan), and meadows (Stoneman, Ahwahnee, Cook’s, Sentinel, Leidig, El Capitan, and Bridalveil).

There is a scenic interface of river, rock, meadow, and forest throughout the Valley. This feature is an important scenic resource recognized throughout Yosemite Valley and found at Happy Isles. The dramatic rock walls that rise above the Merced River in the vicinity of Happy Isles include the base of several prominent rock formations, such as Mt. Broderick, Half Dome, Glacier Point, North Dome, and Washington Column, as discussed above. However, views of waterfalls and rock cliffs from the Merced River in the immediate vicinity of Happy Isles are somewhat limited due to the high valley walls and forest cover.

Recreation

Recreation in Yosemite National Park is guided by the National Park Service’s enabling legislation, which has two purposes: to preserve Yosemite’s unique natural resources and scenic beauty and to make these resources available to visitors for study, enjoyment, and recreation. Visitation to Yosemite has grown substantially in recent years to nearly 4 million visitors annually, a steady increase from 2 million annual visitors two decades ago. Each visitor is looking for an individual experience while entering an increasingly crowded environment.

Recreational Opportunities in Yosemite Valley

Yosemite Valley offers opportunities to experience a spectrum of river-related recreational activities, from nature study and sightseeing to hiking and enjoying solitude and natural sounds along the river. Recreational opportunities include both passive and active recreational activities. Passive recreational activities include photography, nature study, sightseeing, and attending interpretation programs. Active recreational activities in Yosemite Valley include walking/hiking, bicycling, stock use, swimming/wading, fishing, rafting, kayaking, picnicking, camping, rock climbing, cross-country skiing, and ice skating. Recreational opportunities specific to the Happy Isles area are discussed below.

Recreational Opportunities in the Happy Isles Area

The Happy Isles area is a popular recreation destination for Yosemite visitors. Activities include visiting the Nature Center at Happy Isles, nature study at Happy Isles, and hiking the John Muir and Mist Trails. Generally, recreational activities at Happy Isles include sightseeing, walking/hiking, bicycling, stock use, picnicking, photography, nature study, and attending interpretive programs. Activities specific to the Happy Isles Gauging Station Bridge area are further described below.

Sightseeing

According to a study of visitors exiting the park, about 90% of visitor groups reported sightseeing as an activity their parties participated in while in the park (Gramman 1992). Sixty percent of visitor parties took photographs, and more than half reported nature study as an element of their trip. Sitting or standing quietly, absorbed in thought or in awe of one of Yosemite’s majestic views, was found to be basic to the park experience. Artistic pursuits and wildlife viewing were also important to the enjoyment of the park. Sightseeing is a popular pursuit at the Happy Isles area. Many park visitors stop at the Nature Center at Happy Isles near the Happy Isles Gauging Station Bridge to view museum exhibits pertaining to the natural environment of Yosemite. The Yosemite Valley segment of the Merced River provides magnificent views from the river and its banks of waterfalls (Nevada, Vernal, Illilouette, Yosemite, Sentinel, Ribbon, Bridalveil, and Silver Strand), rock cliffs (Half Dome, North Dome/Washington Column, Glacier Point, Yosemite Point/Lost Arrow Spire, Sentinel Rock, Three Brothers, Cathedral Rock, and El Capitan), and meadows (Stoneman, Ahwahnee, Cook’s, Sentinel, Leidig, El Capitan, and Bridalveil). There is a scenic interface of river, rock, meadow, and forest throughout this river segment.

Walking, Hiking, Bicycling, and Stock Use

Walking and hiking are popular activities in the Valley, from a short stroll to the base of Lower Yosemite Fall to a 17-mile round-trip day hike to the top of Half Dome. About 35 miles of hiking trails are available on the Yosemite Valley floor; approximately 22 miles are shared with horseback riders, and 12 miles are shared with bicyclists. A leg of the Valley Loop Trail between Curry Village and Sentinel Bridge is shared with both bicyclists and horseback riders. There are several walking loops in the east Valley, and two loops in the western end: one between Swinging Bridge and the El Capitan Bridge, and between El Capitan Bridge and Pohono Bridge.

Multiple trails lead from the Valley floor to wilderness areas above, the most popular being the Mist and John Muir Trails alongside the Merced River, the Upper Yosemite Fall Trail, and the Four Mile Trail to Glacier Point. Each of these is also popular for backpackers starting multi-day trips into Yosemite’s wilderness and beyond. Until the flood in January 1997, the Happy Isles Gauging Station Bridge served as an approach to the trailhead for the 211-mile John Muir Trail between Yosemite Valley and Mt. Whitney in Sequoia National Park, one of the Sierra Nevada’s most prominent trails. The John Muir Trail was built by the state of California, the Sierra Club, the U.S. Forest Service, and the National Park Service between 1915 and 1938, with the Yosemite section following existing trails. Millions of visitors have used this trailhead near the Happy Isles Gauging Station Bridge to access the Mist Trail, and the Vernal and Nevada Falls Trails. From the Mist Trail and John Muir Trail junctions at the top of Nevada Fall, hikers can access the Panorama Trail to reach Glacier Point and the Half Dome Trail.

Bicycling is a common means for enjoying and exploring Yosemite Valley. In the 1992 Gramman Study, about 11% of visitor surveyed included bicycling in their activities while in the park, mostly in Yosemite Valley. Bicycles are allowed only on paved trails and roads. More than 12 miles of multi-use bicycle trails have been constructed in Yosemite Valley. A multi-use (bicycle and pedestrian) trail links Yosemite Lodge to the Happy Isles area on both sides of the Merced River. Some road segments, such as Happy Isles Loop Road and Mirror Lake Road, are closed to most private vehicle traffic and provide relatively safe bicycle access.

Both commercial and private stock uses are currently found in Yosemite Valley. Except where posted, all designated trails in the park are open to stock and are maintained to accommodate stock traffic. Stock can be used on nonpaved paths that connect the east and west Valley, but paved roads and trails generally may not be used, except where crossing is necessary. Stock use is permitted on the John Muir Trail.

Picnicking

Picnicking in the Valley takes the form of lunch on riverside boulders, a bench near the visitor center, or a shady spot along a wilderness trail, as well as automobile-based picnicking on a tailgate or with charcoal, grills, and coolers. A large number of visitors use a picnic area during their visit to the park. Four designated picnic areas (providing grills, picnic tables, etc.) are provided in Yosemite Valley, including Cathedral Beach, Sentinel Beach, El Capitan, and Swinging Bridge. Church Bowl, near Yosemite Village, has picnic tables only and serves as an informal picnic site.

Swimming and Wading

Swimming and wading in the Merced River are popular activities in Yosemite Valley, including river locations near lodging areas, campgrounds, and day-use areas. Happy Isles Gauging Station Bridge is a favorite location for swimming and wading.

Photography and Nature Study

Many park visitors come to Yosemite Valley specifically to photograph the spectacular scenery and study Yosemite’s diverse natural and cultural history. The Happy Isles area is a popular destination for visitors, providing opportunities for solitude while allowing visitors to observe the braided river channel at Happy Isles. Other local features include the 1996 rockslide area with its wayside exhibits, and the Nature Center at Happy Isles.

Interpretative Programs

The National Park Service provides interpretive programs to the public to inform and educate visitors about the relationship of park ecosystems and the importance of stewardship and resource protection. The Nature Center at Happy Isles is one of the most popular interpretive centers in Yosemite Valley. Located in what was once the Yosemite Fish Hatchery (built in 1927), the center provides family-oriented, interactive educational exhibits on the natural history of Yosemite.

Nearby are short trails focusing on the Happy Isles area’s four different environments—forest, river, talus, and fen. The Junior Ranger Fire Circle, located just across the fen from the Nature Center, often hosts evening campfires for visitors and their families.