2025-08-01_PERMIT FILE - C1981019

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RULE 2 PERMITS South Taylor – Rule 2, Page 11 Revision Date: 7/21/25 Revision No.: MR-267 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 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 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 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 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. Starting on the north end of the permit area, the Axial Basin anticline is an asymmetrical fold, the axis of which trends north 60° west, with strata dipping (inclining) steeper on the south side of the axis than on the north. The rocks of the broad anticline have not been stressed sufficiently to cause them to break severely, but a few discontinuous normal faults trending primarily parallel to the anticlinal axis are found in the area. The south flank of the anticline has several secondary folds trending subparallel and at approximate right angles to the main anticlinal axis. The axis of the Collom syncline, a downward fold approximately parallel with the Axial Basin Anticline, passes north of the existing Colowyo mine and permit revision area. Bedding orientation, as measured on surface outcrops, has a strike of around N 70° W. Dips on the shared limb with the Axial Basin anticline can exceed 45°, but are normally between 25° and 35° and dip to the south. The south flank of the syncline has dips between 5° and 20° to the north (Map 7A).