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Map 1: The approximate 11,200 acre Trapper Mine permit boundary and the area's typical <br /> pre mine dendritic drainage pattern as per the NHD, the National Hydrology Dataset. <br /> Ph.. siygraphic Setting <br /> Trapper Mine extends across the northern slope of the Williams Fork Mountains between <br /> elevations of 6,500 ft. and 7,800 ft. The crest of the Williams Fork Mountains forms a long <br /> ridge extending east/west at elevations between 7,400 and 7,800 ft. The Yampa River flows <br /> generally from east to west a short distance north of the permit area. The Williams Fork River <br /> skirts the south side of the mine site and flows into the Yampa River one mile west of the <br /> mine. <br /> Geologic Setting <br /> The bedrock at the ground surface in the Trapper permit area is an interbedded sequence of <br /> sandstones, siltstones, shale, and coals comprised of the Cretaceous-age Williams Fork <br /> Formation. The Williams Fork Formation forms part of the regionally extensive Mesa Verde <br /> Group. Younger unconsolidated alluvial deposits of Quaternary age form a thin mantle over the <br /> Williams Fork Formation in stream drainages. Structurally, the mine is situated on the south <br /> limb of the northwest-plunging Big Bottom syncline. Major faults extend across the region, <br /> but none have been found in the permit area. <br /> Coal Seam Stratig_rWhy <br /> The Williams Fork Formation is stratigraphically subdivided into three units or members. These, <br /> in ascending order are: <br /> 1. the lower Williams Fork <br /> 2. the Twentymile sandstone <br /> 3. the upper Williams Fork <br /> with individual thicknesses of 920 ft. 100 ft. and 680ft. respectively. The coal seams being <br /> mined at Trapper Mine are all in the upper Williams Fork member and their nomenclature, in <br /> descending order, consists of- <br /> 0 H <br /> o I <br /> o L <br /> o Q <br /> o Q rider <br /> o R and R rider. <br /> Surface Water Hydrology <br /> Drainages within and adjacent to the permit area (on the north facing slope) drain south to north <br /> in a dendritic pattern as illustrated in Map 1 above. Drainages flow primarily in response to <br /> snowmelt and/or heavy rains,eventually discharging to the Yampa River. Drainages in the <br /> southern portion of the permit area drain southward to the Williams Fork River. Natural surface <br /> waters are of a calcium-magnesium-sulfate type, with total dissolved solids content commonly <br /> greater than 1000 mg/1 in the smaller streams, and less than 1000 mg/1 in the largest streams. <br /> Total dissolved solids concentrations commonly peak during periods of low stream flows; during <br /> high flows, waters are diluted, resulting in low concentrations. <br /> Ground Water Hydrology <br /> 8 <br />