2013-04-10_PERMIT FILE - C1981019A (10)

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RULE 2 PERMITS environment, with the sedimentation influenced by sea -level changes, indicated by the presence of both marine and non- marine rocks. The group consists of the Iles and the Williams Fork Formations and overlies the Mancos Shale. Carbonaceous rocks are present in both formations; however, in the area of the Colowyo Mine, thick coal beds are found only in the Williams Fork Formation. Iles Formation - The Iles Formation conformably overlies the Mancos Shale. It is exposed on the edges of the Axial Basin and south and west of the Colowyo revised permit area in the Wilson Dome area. It has a thickness of approximately 1,500 feet. It is composed of littoral sands deposited along a regressional ocean margin. The Iles is generally comprised of light brown- to white, fine- to medium - grained, poorly sorted calcareous sandstone interbedded with red and dark maroon sandy and silty carbonaceous shale. Thin lenticular coal beds are found in the formation. A thick sandstone at the top of the Iles Formation, the Trout Creek Sandstone Member, is a reliable marker horizon for drill holes in the Danforth Hills and surrounding areas. The Trout Creek Sandstone is light - colored, fine- grained, well - sorted, massive sandstone that was deposited in a marginal- marine or littoral environment. The thickness of the Trout Creek Sandstone varies across the area but is generally 60 to 80 feet. The deposition of the Trout Creek Sandstone marked a major regression of the Late Cretaceous seaway in this region. The resulting clean blanket sand formed by this migrating beach and barrier island complex is an aquifer of regional extent in northwestern Colorado. The Trout Creek Sandstone Member, a common ridge - forming unit in the Danforth Hills, has been called the "White Rock" because of its characteristic white sandstone exposures. The Trout Creek sandstone underlies the lowest surface recoverable seam to being mined at South Taylor (the G789 seams) by approximately 590 feet. Williams Fork Formation - The Williams Fork Formation is the predominant coal- bearing unit in the Colowyo revised permit area. The formation conformably overlies the Iles Formation. The Williams Fork consists of a typical lagoonal sequence of interbedded tan to light gray sandstones, light gray to gray siltstones, sandy, silty, or carbonaceous gray mudstones and coals. This sedimentary sequence is an example of cyclothems deposited along a linear clastic shoreline located at the edge of an epicontinental seaway. The formation ranges from beach sands grading into lowermost deltaic sediments deposited by sluggish brackish water at the base, to middle and upper deltaic deposits deposited in a bayou setting in the upper portions of the formation. This sequence was formed as the shore transgressed seaward, resulting in the gradation from marine sediments below the formation to terrestrial sediments above the formation. 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 Colowyo revised 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 Colowyo revised 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 Collom permit expansion area. A facies change within the Williams Fork Formation has eliminated the Twenty Mile Sandstone in the Danforth Hills Area. Collom — Rule 2, Page 28 Revision Date: 9/28/11 Revision No.: PR -03