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evaluate these surface finds for inclusion on the National <br />Register of Historic Places (NRHP); to determine the potential <br />effect of the mining activities on all NRHP-eligible <br />resources; and to make recommendations for the mitigation of <br />the adverse effects on those cultural resources. <br />Location of the Study Area <br />The study area is in the west-central portion of Colorado <br />just north and east of the town of Somerset. It is located in <br />T. 13 S., R. 90 W., Sections 1, 2, 3, 4, 9, 10, 11 and 12, 6th <br />P.M. (Figure 1). <br />Environment <br />The study area lies within the Piceance Basin, a major <br />geologic subdivision of western Colorado. The basin is an <br />elongate structural downwarp of the Colorado Plateau province <br />that apparently began its subsidence approximately 70 million <br />years ago during the laramide orogeny. Sediments from <br />surrounding highlands were deposited in the basin, <br />accumulating to a thickness of as much as 9000 feet by the <br />• lower Eocene epoch, when subsidence ceased. Regional uplift <br />occurred in Late Tertiary time, and erosion of the area has <br />continued since (Young and Young 1977). The study area lies <br />off the southeast corner of Grand Mesa, an 11,000-foot high, <br />flat-topped mountain capped by basalt flows of late Miocene <br />and early Pliocene age (about 10 million years old). The <br />Cretaceous-age Mesaverde Formation sandstones and coal-bearing <br />rocks make up the study area. <br />Hawksnest Creek, a tributary wash of the North Fork of <br />the Gunnison River, cuts through the study area. Elevations <br />in the study area range between 6000 and 8400 feet. These and <br />the surrounding higher elevations support two main plant <br />communities: Transitional Zone (oakbrush, serviceberry, <br />scattered pinyon and juniper) on the mountain sides, and <br />riparian woodland and sagebrush/grassland in the narrow valley <br />bottoms. Vegetation cover in the project area is primarily <br />oakbrush and ground visibility is about 30 percent. The <br />region supports numerous wildlife species. Elk, deer, coyote, <br />black bear, rabbits and raptors are common. <br />Climatically, the yearly average temperature is 51 <br />degrees F., and there is a maximum of 120 frost-free days in a <br />year. Annual precipitation is about 12-15 inches (USDA SCS <br />• 2 <br />