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• TOPOGRAPHY AND HYDROtOCY <br />The following brief sketch of the environment of the Yoast area is intended to provide <br />information on the important characteristics of local hydrology, elevation, and <br />topography. <br />The project area is underlain by the Upper Cretaceous Williams Fork formation, consisting <br />of sandstone, shale, and coal. The Upper Cretaceous Iles Formation (Heil et al., 1977), <br />stratigra phically under the Williams Fork Formation, also consists of sandstone, shale, <br />and coal. These formations are part of an anticline running northeast/southwest through <br />the study area. <br />Dominant soils are formed in materials weathered residually from shale, while less <br />extensive soils are formed in aeolian and alluvial deposits. Bo rollic Camborthids <br />comprise about 65 percent of the soils in the area, while Ari dic Agri bo rolls comprise <br />about 35 percent (Heil et al., 1977). <br />• The project area is located at the northern fringe of the Williams Fork Mountain Range to <br />the north of the Yampa River Valley. Twenty-mile Park borders the study area to the east, <br />and Dunkley Park (a basin-like area) is to the south. Along the western edge of the <br />southern portion of the area is Sage Creek and its flood plain which contains an altered <br />vegetation community that supports livestock grazing. Intermittent drainages are present <br />throughout the project area with eastern drainage into Grassy Creek and the rest <br />accumulating in Sage Creek. Both Cra ssy and Sage Creeks flow approximately seven miles <br />north to the Yampa River. <br />Elevations in the study area range from 6,960 ft (2,117 m) in the extreme north to 7,960 <br />ft (2,421 m) in the extreme southwest corner. The area is one of high reliefp steep <br />slopes and ridges are separated by alluvial valley floors. <br />• <br /> <br />