2016-11-18_PERMIT FILE - C1981019A (7)

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RULE 2 PERMITS The Williams Fork Formation is the predominant coal -bearing unit in the Mesaverde Group. The coal beds in the formation are uniformly distributed near the mine but generally vary in thickness and extent away from the current Colowyo mine area. The coals are part of the Fairfield Coal Group. The natural, pre -historic burning of underlying coal beds has baked areas of the Williams Fork Formation within the permit area and the adjacent area. These surface areas are easily distinguished by their red -brown to orange -brown color on the surface. These coal burns are known to extend into the rock for up to several hundred feet. The stratigraphic thickness of the Williams Fork Formation in the permit area is about 1,700 feet. Although the formation contains some thick sandstone layers, the Twenty Mile Sandstone Member (within the Williams Fork Formation in the Craig, Hayden, and Steamboat Springs areas) is not present in the permit area. A facies change within the Williams Fork Formation has eliminated the Twenty Mile Sandstone in the Danforth Hills Area. A distinctive bed in the formation is a smectite layer, with an average thickness of two to three feet. Formed from the deposition of a volcanic ash, Colowyo has identified this bed as the `Km'. (This bed may be equivalent to the Yampa Bed in the Williams Fork to the north). The bed has been identified as an aquiclude. This bed is approximately 165 feet above the top of the Trout Creek Sandstone. It underlies the lowest seam proposed to be mined by at least 330 feet. Thus, there should be no impact from the mining operations to the underlying Trout Creek Sandstone. The upper Williams Fork Formation is composed of upper and middle deltaic sediments in the vicinity of the Colowyo Mine. This is evidenced by an increase in mudstone and less continuous sandstone layers than is found at other locations in the region (Kiteley, 1983; Geocid, 1998). Coarse-grained sediments in the proposed mining area are typified by channel and bay -fill sandstones. These are of limited extent and laterally discontinuous. Structure The regional geologic structure of the Danforth Hills is a complex of folds dominated by the Axial Basin Uplift to the north of the existing Colowyo mine and South Taylor/Lower Wilson mining areas and the Piceance Basin on the south. The Axial Basin Uplift, an anticline, or arch, is a southeastward extension of the larger Uinta Mountain Arch to the west, which trends west by northwest. Between the Axial Basin anticline and the basin is a series of synclines, anticlines, and monoclines. The permit area is located between the Axial Basin anticline on the north and the Danforth Hills anticline /Wilson Creek dome to the south. The southern limb of the Axial Basin anticline is shared with the Collom Syncline. The current Colowyo operation is on the southern flank of the Collom syncline. Southwest of the proposed permit area is the Danforth Hills Anticline/Wilson Creek Dome. Southeast and east of the permit revision area is the Elkhorn Syncline. A small unnamed anticline is located beneath the permit revision area. An unnamed syncline exists along the West Fork of Good Spring Creek. These structures are affected by the Elkhorn Syncline on the east, which results in an eastward to southeastward downward dip in the South Taylor area (Map 7A). The springs in the West Fork of Good Spring Creek are the result of converging bedrock dips caused by this unnamed syncline. South Taylor/Lower Wilson — Rule 2, Page 12 Revision Date: 11/18/16 Revision No.: MR -163