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• <br />ENVIRONMENTAL DESCRIPTION <br />The study area* is underlain by the Williams Fork <br />formation, Upper Creteaceous in age, consisting of sandstone, <br />shale, and coal, and the Iles formation, Upper Creteaceous <br />in age, stratigraphically under the Williams Fork formation 11 <br />also consisting of sandstone, shale, and coal (see Tables 2 <br />and 3). The crest of an anticline** runs from northwest <br />to southwest through the study area (see Map 3). <br />The climate of western Colorado can be characterized <br />as highland, with generally cool temperatures (Berry 1968). <br />Topography is the most complex factor in mountain climates <br />with western and southern slopes being generally warmer than <br />are eastern and northern slopes (Armstrong 1972). Craig <br />receives 12 inches of rain per year, while Steamboat Springs ~ <br />receives 24.5 inches (US Weather Bureau 1964). The study area ~ <br />• is located tetween Craig and Steamboat, suggesting that average <br />annual rainfall is between 12 and 24.5 inches per year. The <br />average annual temperature ranges from +92 to -25 degrees <br />Fahrenheit. <br />Dominant soils are formed in materials weathered <br />residually from shale, while less extensive soils are formed <br />in aeolian and alluvial deposits. Borollic Camborthids make <br />up about 65% of the soils of the area, while Aridic Agri- <br />borolls make up about 357a (Heil et al. 1977). <br /> <br />* The study area is located about four miles south of the <br />Yampa River along the western edge of Twenty Mile Park, and <br />along the northern edge of the Williams Fork Mountains (see <br />Maps 1, 2, and 5). Elevation ranges from 8,106 feet in the <br />northeast corner of the project area to about 6,900 feet in <br />the south. The area can be characterized as one of high <br />relief, from big sage and snowberry covered alluvium to <br />scrub oak and chokecherry covered ridgetops. Several small <br />ephemeral drainages flow from the center of the project area <br />• to the west, south, and east into Fish or Grassy Creeks, and <br />ultimately the Yampa River. <br />** Please see the Glossary for definition of this and other <br />archaeological terms used in this report. <br />3 <br />