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RULE 2 PERMITS <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 />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 />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 />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 />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 />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 />South Taylor/Lower Wilson — Rule 2, Page I I Revision Date: 11 / 18/16 <br />Revision No.: MR -163 <br />