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n~~o'}/1: U ,J_ ...:v !,:j);~~II.FI!I.~;I:i~j:.lllal.I;:!E.JlII.I:I..J!~;~~ INTRODUCTION This chapter describes the physical, biological, social, and economic aspects of the existing environment potentially affected by implementation of alternative actions, Council on Environmental Quality (CEQ) regulations direct agencies to describe the environment that could be affected commensurate with the importance of the impacts (40 CFR 1502.15). The data and level of detail presented in this chapter are, therefore, based on the information necessary for the reader to compare the existing situation with the potential effects of the alll7natives. The description of the existiog environment is structured by resource. The topics are discussed in the same order in chapters 3 and 4 to facilitate COmparisolL In order to fully understand the impacts of alternative actions on a specific resource, the reader should first read the applicable section of Chapter 3 and then the corresponding sections in Chapter 4. The assessment area for this Environmental Impact Statement (EIS) varies by resource according to the natural limits of influence of each resource. For all resources, it includes the project area, which is dermed by the Aspen Highlands special use permit (SUP) area. For detailed technical descriptions, and for analytical methods used for a specific resource area, readers are referred to the technical report for that resource, where applicable. All technical reports are available from the Aspen Ranger District, White River National Forest, Aspen, Colorado. Since the base area development proposed by Hines would occur with or without any future on-mountain development but is not explicitly part of Alternatives B and C, it is described in this chapter only to the extent that it would affect skier access to and egress from the Aspen Highlands Ski Area, GEOLOGY AND SOILS 1bis section summarizes the geology, geological hazards, and soil limitations associated with activities proposed for Aspen Highlands. A description of these aspects was presented by McCalpin (1994), and further field studies were conducted in September/October 1995 to investigate the geologic hazards and soil units that could affect the natural environment and human activities in the ski area. GEOLOGIC SETTING Aspen Highlands consists of a bedrock ridge that dips 25 to 400 to the northeast, which is flanked by Castle Creek to the east and Maroon Creek to the west. The Elk Mountains, which contain Aspen Highlands, are composed of a thick sequence of late Paleozoic and Early Mesozoic sedimentary rocks. The thickest of the sedimentary units is the Maroon Formation, a Pennsylvanian-Permian assemblage of red sandstones, siltstones, and conglomerates, that reaches a thickness of 14.500 feet to the north of Aspen (Bryant 1979), and underlies about half of the ski area. The shape of the ridge together with the strength of the Paleozoic formations provide considerable slope stability, despite the steep slopes and valleyward dip of bedding. figure 3.1 shows the 10 bedrock formations found in the Aspen Highlands Ski Area, as well as 15 unconsolidated deposits, all of which are of Quaternary age (the past 2 million years) and include alluvial deposits (mainly stream deposits and terraces), glacial deposits (till and outwash), and mass-movement deposits (landslides, talus, and colluvium). Glacial units were mainly deposited in the last glaciation of this area, about 15,000-20,000 years ago. The alluvial and mass movement deposits are younger, and were deposited across a landscape strongly shaped by the glaciers. The reader is referred to the Geology, Geologic Hazards, and Soil Hazards Technical Report (Geo-Haz 1996) for a full detailed description of each bedrock unit. Geology and Soils Geologic Selling 3-1