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-4- <br />Description of the Environment (con't) <br />Coal mined by the operation is within the upper unit of the [Jilliams Fork <br />Formation. The coals are separated by siltstones, mudstones and sandstones. <br />At the base of the upper unit of the Williams Fork Formation, 200 to 300 <br />feet below the coal zone, is the 100 foot thick ledge forming Twenty Mile <br />sandstone. The Twenty Mile sandstone outcrops below the southern end of <br />the mine site. <br />The Twenty Mile sandstone and lower lying Trout Creek sandstone are aquifers <br />of significant regional extent. Other ground water bearing zones occur in <br />the coals and local lenticular sandstones within the mining area. Recharge <br />areas for most of these strata are on the south facing slopes along the <br />Williams Fork River Valley south of the mine. Ground water tends to flow <br />along the dip of the strata (northeast) and some of the localized lenticular <br />sandstones discharge in the form of springs north of the mine. <br />Within the permit area are portions of the Hayden Gulch, Dowden Gulch and <br />Dry Creek drainage basins. The majority of the mine area occurs within the <br />Hayden Gulch drainage. These basins contain ephemeral streams which respond <br />predominantly to spring runoff from snowmelt. Hayden and Dowden Gulch are <br />tributaries to the Williams Fork River which is perennial in nature. <br />The region is characterized by a semiarid steppe climate regime. The <br />prevailing wind is from the west and southwest and average annual precipatation <br />is 16.1 inches. The growing season in the region varies from 28 days to <br />94 days; the time span depending greatly upon the elevation of particular areas. <br />Soils at the mine site are of the order mollisol and suborder boroll. These <br />are soils formed in cool climates which are characterized by a very dark <br />colored base-rich surface layer. Variability of the characteristics of the <br />soils on the permit area is primarily due to slope, aspect and topographic <br />position. Deeper soils are located in the valley bottoms and footslopes <br />while the shallower soils occupy the upslopes. <br />Vegetation is also distributed in response to the micro climate influences <br />of the north-south trending ridge and valley complex within the area. <br />Sagebrush communities dominate the richer, deeper soils of the valley bottoms <br />and gentle slopes. Oak communities dominate the generally drier south and <br />west facing slopes in the area, and often intergrade into the other communities <br />in the form of patches of dense oak growth. Aspen dominated communities are <br />found in clumps in small hillside swales and gentle north slopes in the <br />permit areas; these areas are characterized by a more mesic moisture regime <br />and more fertile soils. The remaining mountain shrub can be subdivided into <br />two distinguishable components; communities dominated by chokecherry, and <br />communities dominated by serviceberry. Serviceberry communities are found <br />dominating steep south facing slopes in the southern mine permit area. These <br />areas are characterized by a relatively xeric moisture regime and poorly <br />developed soils receiving large amounts of high intensity solar radiation. <br />Chokecherry communities are found on the gently sloped hill tops in the area. <br />These communities intergrade with the aspen, sage, and oak communities. <br />