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• <br />inventory. All of the isolated resources are recommended as "not eligible" to the NRHP. The <br />inventory was conducted as a "non - collection' inventory with field analysis /documentation of all <br />artifacts. <br />EFFECTIVE ENVIRONMENT <br />This project is located toward the north end of Twentymile Park and in the upper valley of <br />tributaries of Sage Creek in the foothills of the Williams Fork Mountains approximately six miles <br />south of the Yampa River in Northwest Colorado. In general the area is a high plateau with <br />rugged mountainous areas, broad valleys, and rolling upland parks. The area is drained by a <br />dendritic pattern of seasonal drainages flowing generally east and south to Fish Creek, a tributary <br />of Trout Creek which flows north to the Yampa River. <br />Quaternary deposition in the project area is mostly alluvial with some areas of colluvium. <br />Dark brown silts and sandy silts up to several meters thick have accumulated in the drainage <br />bottoms. Holocene deposits on the tops and upper slopes of the low ridges are thin and consist of <br />light to medium brown silty loams. The rugged hilly areas surrounding Twentymile Park contain <br />thick colluvial deposits on the slopes and adjacent to drainage bottoms. Alluvium has <br />accumulated in the drainage bottoms and thin aeolian deposits have accumulated in the hills, <br />especially on the leeward sides of ridges. <br />., The project area is situated at the west edge of a structural syncline underlain by <br />Cretaceous age Lewis Shales and sandstones, coal beds and shales of the Williams Fork Formation <br />(Tweto 1979). The tops of the high ridges, knobs and hills surrounding Twentymile Park are <br />capped by the thick, light colored Twentymile sandstone. Outcroppings of the Twentymile <br />sandstone in the area are the frequent locations of rock art panels and rockshelters (Pool 1997). <br />Although sandstone outcrops in the project area, no cliff faces suitable for rock shelters or rock art <br />occur. <br />Stands of aspen trees and thick shrubs are found at the higher elevations on north facing <br />slopes while sagebrush, grasses, and mixed forbs are found in the parks and along drainages at the <br />lower elevations and on south facing slopes. Vegetation cover in the project varied from 100% to <br />40 %. Some of project area is improved range where the native sagebrush has been replaced by a <br />mix of native and non - native cattle forage. Area fauna includes a variety of large ungulates, black <br />bear, coyote, fox, and several species of small and medium -sized mammals. Numerous avian <br />species also inhabit or utilize the area. <br />At present, the area is used predominantly for ranching, agriculture, and coal mining. <br />Large portions of the parks and valleys appear to have been mowed and /or plowed in the past and <br />cattle grazing is ongoing. The project area is rich in natural resources that would have been <br />attractive to the Native American inhabitants during prehistory <br />For Official Use Only: Disclosure of Site Locations Prohibited (43 CFR §7.18) <br />4 <br />• <br />