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RULE 2 PERMITS <br /> <br />South Taylor – Rule 2, Page 10 Revision Date: 7/21/25 <br /> Revision No.: MR-267 <br />inundated by an epeiric seaway during the late Cretaceous. The Mancos Shale is generally more than <br />3,000 feet below ground surface in the permit area and is about 1,700 feet below the base of projected <br />mining. <br /> <br />Mesaverde Group - The Mesaverde Group generally consists of interbedded sandstones, mudstones and <br />siltstones of varying thicknesses. These beds were deposited in predominantly a near-shore terrestrial <br />environment, with the sedimentation influenced by sea-level changes, indicated by the presence of both <br />marine and non-marine rocks. The group consists of the Iles and the Williams Fork Formations and <br />overlies the Mancos Shale. Carbonaceous rocks are present in both formations; however, in the area of <br />the Colowyo Mine, thick coal beds are found only in the Williams Fork Formation. <br /> <br />Iles Formation - The Iles Formation conformably overlies the Mancos Shale. It is exposed on the edges <br />of the Axial Basin and south and west of the permit area and active mine in the Wilson Dome area. It has <br />a thickness of approximately 1,500 feet. It is composed of littoral sands deposited along a regressional <br />ocean margin. <br /> <br />The Iles is generally comprised of light brown- to white, fine- to medium-grained, poorly sorted <br />calcareous sandstone interbedded with red and dark maroon sandy and silty carbonaceous shale. Thin <br />lenticular coal beds are found in the formation. A thick sandstone at the top of the Iles Formation, the <br />Trout Creek Sandstone Member, is a reliable marker horizon for drill holes in the Danforth Hills and <br />surrounding areas. <br /> <br />The Trout Creek Sandstone is light-colored, fine-grained, well-sorted, massive sandstone that was <br />deposited in a marginal-marine or littoral environment. The thickness of the Trout Creek Sandstone <br />varies across the area but is generally 60 to 80 feet. The deposition of the Trout Creek Sandstone marked <br />a major regression of the Late Cretaceous seaway in this region. The resulting clean blanket sand formed <br />by this migrating beach and barrier island complex is an aquifer of regional extent in northwestern <br />Colorado. The Trout Creek Sandstone Member, a common ridge-forming unit in the Danforth Hills, has <br />been called the "White Rock" because of its characteristic white sandstone exposures. <br /> <br />The Trout Creek sandstone underlies the lowest surface recoverable seam to be mined at South Taylor <br />(the G789 seams) by approximately 590 feet. <br /> <br />Williams Fork Formation - The Williams Fork Formation is the predominant coal-bearing unit in the area <br />of the active mine and the permit revision area. The formation conformably overlies the Iles Formation. <br />The Williams Fork consists of a typical lagoonal sequence of interbedded tan to light gray sandstones, <br />light gray to gray siltstones, sandy, silty, or carbonaceous gray mudstones and coals. This sedimentary <br />sequence is an example of cyclothems deposited along a linear clastic shoreline located at the edge of an <br />epicontinental seaway. The formation ranges from beach sands grading into lowermost deltaic sediments <br />deposited by sluggish brackish water at the base, to middle and upper deltaic deposits deposited in a <br />bayou setting in the upper portions of the formation. This sequence was formed as the shore transgressed <br />seaward, resulting in the gradation from marine sediments below the formation to terrestrial sediments <br />above the formation. <br /> <br />The Williams Fork Formation is the predominant coal-bearing unit in the Mesaverde Group. The coal <br />beds in the formation are uniformly distributed near the mine but generally vary in thickness and extent <br />away from the current Colowyo mine area. The coals are part of the Fairfield Coal Group. The natural, <br />pre-historic burning of underlying coal beds has baked areas of the Williams Fork Formation within the <br />permit area and the adjacent area. These surface areas are easily distinguished by their red-brown to <br />orange-brown color on the surface. These coal burns are known to extend into the rock for up to several <br />hundred feet.