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RULE 2 PERMITS <br />2.04.6 Geology Description <br />The coal to be mined in the permit area is located in the northern extent of the Danforth Hills coalfield of <br />the Uinta Region. The Danforth Hills coal field comprises the coal deposits on the northeast flank of the <br />Piceance Creek basin and is bordered on the northeast by the Axial Basin Anticline. <br />The general stratigraphy within the permit revision area is shown on figures 2.04.6-3A and 2.04.6-313, and <br />is graphically shown on figures 2.04.6-4A through 2.04.6-4F. The locations of the geologic cross <br />sections are shown on Map 7A. <br />Coal seams X and A through G789 will be mined in the South Taylor area. The coal seams to be mined in <br />the Lower Wilson pit are anticipated to be the G, H, I, and J seams and splits of these seams. The <br />thicknesses of these seams are shown on figures 2.04.6-3A and -313. <br />The coal to be mined has a high BTU value of 10,000 to 11,000 BTU per pound, low sulfur, and low ash <br />content. It is in generally discreet seams of mineable thickness. There exists a market for this coal, in <br />part because of its ideal qualities. The analyses of the coal seams to be mined are considered confidential <br />and are provided in the original permit application and will be provided to the Division under separate <br />cover. <br />Stratigraphy <br />The permit area is underlain by as much as 13,500 feet of sedimentary rock consisting of approximately <br />4,500 feet of Paleozoic quartzite, limestone, shale, sandstone, and gypsum; and 9,000 feet of Mesozoic <br />limestone, shale, mudstone, sandstone, and conglomerate (Hallgarth, 1959). The coal seams mined at the <br />Colowyo operation are of Upper Cretaceous Age. <br />The generalized geological setting is shown on Map 7A. The stratigraphic positions of the coals mined <br />by Colowyo are illustrated in Figure 2.04.6-3A and Figure 2.04.6-313. <br />The surficial geologic formations within the area are the Upper Cretaceous Mancos Shale, which is <br />overlain by the upper Cretaceous Mesaverde Group. The Mesaverde Group is comprised of the Iles <br />Formation and Williams Fork Formation. Details of each formation are described below. <br />Mancos Shale — This thick marine formation is the oldest exposed unit in the area and is located north of <br />the active Colowyo mine area in the Axial Basin. The formation is approximately 5,000 feet thick, <br />consisting predominantly of a calcareous lower phase and an upper phase that contains a few thin bedded, <br />tan, silty fine-grained sandstone layers within massive sandy shale. The deposition of the Mancos Shale <br />occurred in quiet offshore conditions when the western interior of the North American continent was <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 />South Taylor/Lower Wilson — Rule 2, Page 10 Revision Date: 4/7/17 <br />Revision No.: RN -07 <br />