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ENVIRONMENTAL SETTING The study area is located on the northern edge of the Williams Fork Mountain, just to the south of Hayden, Colorado. Elevation ranges from just less than 6800 feet to just over 7800 feet and slopes generally from southeast to northwest. The area can be charac- terized as one of high relief, from big sage covered alluvial floors to scrub oak covered ridgetops. Drainage is generally southeast to northwest, by many small, seasonal drain- ages running into Hubberson Gulch and then Dry Creek and ultimately, the Yampa River. The area is underlain by the Williams Fork Formation, Upper Cretaceous in age, consist- ing of sandstone, shale, and coal. Soils will not be discussed in detail, see Tab 9, Soil Survey for information on the Seneca II-W soi{s. The soil scientists told the field crew that the alluviation rate was quite rapid (surface deposits 5-10 years in age), that ridge- tops were quite stable, with soil development about 24 inches and 10-100,000 years old, and that a talus slope could be quite stable for the 10-100,000 year time range. I The climate of western Colorado can be characterized as highland, with generally cool temperatures (Berry 1968). Topography is the most complex factor in mountain climates, with western and southern slopes being generally warmer than eastern and northern slopes (Armstrong 1972). Craig receives 15.51 inches of precipitation per year, while Steamboat Springs receives 23.87 inches (U.S. Weather Bureau 1964). The annual precipi- tation for Hayden which is the closest station to_Seneca II-W is 16.11 inches per year. The average annual temperature is 41.9°F for Hayden (Climatological Data; Annual Sum- mary; Colorado 1980). See Tab 8, Climatology, for more information. Vegetation varies with the elevation and topography of the study area. Alluvial bottoms and the lower south to west facing slopes contain the sagebrush grassland community, with wheatgrasses, native and introduced bluegrass species, needlegrasses, and a variety of fortis as component species. Basin big sage occurs in the lower elevations and alluvial areas while mountain big sage occurs at higher elevations. The mountain shrub com- munity is found on steep slopes and ridgetops at generally higher elevations. Choke- cherry, mountain mahogany, serviceberry, Gambel's oak, and snowberry are found in this community. Aspen stands are occasionally found on north to northwest facing slopes, and in drainage bottoms of the eastern to southeastern side of the study area, where eleva- tion is somewhat higher than the western area. 5-3