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<br />13 <br /> <br />high daytime temperatures and low relative humidity, potential evapo- <br /> <br />,..,. ration rates are very high in the summer. Consequently, most of the <br />W <br />~ soil moisture is' supplied by melting snow and low intensity rains in <br /> <br />the winter. <br /> <br />Vegetation is of the salt-desert-shrub type (Bureau of Land <br /> <br />Management, 1978). Black greasewood, mat saltbush, big sagebrush, <br /> <br />and rubber rabbitbrush grow on alluvial soils and along tributaries <br /> <br />of the abundant drainage basins. Upland sandy soils support shad- <br /> <br />scale and galleta. Gardner saltbush is the dominant plant on the shaley <br /> <br />soils (Lusby, et al., 1963). <br /> <br />3.4 Land Use <br /> <br />Land use includes recreational use of off-road vehicles (ORVs), <br /> <br />natural gas and coal exploration and extraction, and grazing. Trails <br /> <br />and roads are abundant. Several watersheds in the vicinity of Grand <br /> <br />Junction and Walker Field are popular ORV sites. Access to turn-of- <br /> <br />the-century Mesa Verde Formation coal mines involved a network of <br /> <br />haul roads and a railroad spur across the Mancos Shale terrain. <br /> <br />Natural gas production in the last three decades has resulted in numer- <br /> <br />ous new access roads and buried pipelines. <br /> <br />Despite the desert environment, the area has been grazed since <br /> <br />the 1880's. Grazing began with cattle herds imported from Texas, and <br /> <br />beginning around 1915, it included large flocks of migratory sheep. <br /> <br />Heavy grazing was restricted in part by the Taylor Grazing Act in <br /> <br /> <br />1934 (Lusby, et aI., 1963). It decreased even more in the 1950's when <br /> <br />trucks began transporting sheep to the high country., The entire <br /> <br />study area is still open range, however, and evidence of livestock <br />