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------------------------------ <br /> � ,.'b �•`. � q:` `' i `w''~v r' 'r r ,{5 °f r�b E..y,e <br /> r� Eagle-Gypsum Mine <br /> A 75 <br /> r <br /> c` tt <br /> i t <br /> i <br /> $ <br /> � r <br /> FIGURE 5.1: GEOLOGICAL MAP(AREA TAKEN EROm TWETO ET AL., 1978) <br /> .3.2 Soils <br /> There is virtually no topsoil at the Mine; vegetation typically grows in areas consisting of <br /> weathered gypsum (gypsite) and residual volcanic ash. Previous permits and investigations <br /> reported depths of volcanic ash ranging in thickness from 3 inches to 2 feet. The MRCS soil <br /> resource report (MRCS, 201 6) shows the proposed Upper Pit expansion and Fast Pit consist of <br /> Soil Group B (Gypsum land—Gypsiorthids complex, 12% to 65% slopes) and Soil Group D <br /> (Torriorthents-Camborth ids-Rock outcrop complex, 6% to 65% slopes). Hydrologic soil groups <br /> are classified by the mininnum rate of infiltration achieved for bare soil after prolonged wetting. <br /> Group A soils have the lowest runoff potential and highest infiltration rates, while Group D soils <br /> have the highest runoff potential and lowest infiltration rates. Group A soils have the lowest <br /> erosion potential and Group D soils have the highest erosion potential (United States Department <br /> of Agriculture(USDA), 1986). <br /> Local terminology for the land type is "Gypsum Badlands'. Existing sparse "topsoil" in the area <br /> consists solely of weathered gypsum (gypsite) and residual volcanic ash. Historically, there has <br /> been virtually no interest in the area for agricultural uses or from the Soil Conservation District. <br /> Ridge topsoils consist primarily of gypsite mixed with weathered residue of other clastic sediments <br /> inter-bedded with the gypsum. Exploration drilling has shown that the clastic sediments do inter- <br /> bed at depth with the gypsum zones. The steep side hill slopes are essentially gypsum rock <br /> 46 <br />