2018-01-03_REVISION - C1994082 (29)

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The Yoast permit area is in the Williams Fork Mountains, within the southeastern synclinal portion of the Sand Wash structural Basin of northern Colorado and central Wyoming. The coal seams that were mined were the Wadge and the Wolf Creek. These seams are contained within the Middle Coal Group, an interval of interbedded sandstones, sandy shales, shales and coal within the Williams Fork Formation. The Middle Coal group also contains the Lennox Coal seam, which was non -commercially mined at the Yoast Mine. Above the Middle Coal Group is the Twentymile Sandstone, a 100-200 foot thick fine-grained, massive sandstone. The upper unit of the Williams Fork Formation, which contains the Upper Coal Group of the Mesaverde group, consists of layers of sandstone, sandy shale, shale and coal. The thickness of the unit varies from approximately 200 to 850 feet throughout the region. The Williams Fork comprises the upper 200 to 850 feet of the Cretaceous Mesaverde Group. Underlying the Williams Fork Formation is the Iles Formation, which is the lower member of the Mesaverde and the oldest unit to outcrop in the permit area. The Iles Formation is approximately 1,500 feet thick. The basal unit of the Iles Formation is the Tow Creek Sandstone, a 35-125 foot thick massive, fine-grained, well -sorted sandstone. Overlying the Tow Creek Sandstone is a 1,200 foot thick interval of interbedded shales, sandstones and coals known as the lower coal group. The Iles Formation is crowned by the Trout Creek Sandstone, which is a massive fine- grained sandstone with a thickness of approximately 100 feet. The Late Cretaceous Mancos Shale underlies the Iles Formation and outcrops southwest of the permit boundary along Sage Creek and the Sage Creek Anticline. The Mancos Shale is a dark grey marine shale with interbedded sandstones near the top and interbedded sandstone and limestone near the bottom. Overlying the Mesaverde Group is the Lewis Shale, a homogeneous marine shale with a thickness of between 1,000 and 1,500 feet. The Lewis Shale is overlain by the Cretaceous Lance Formation and the Tertiary Fort Union Formation. The Eocene Wasatch Formation unconformably overlies the Fort Union Formation. It is comprised primarily of fresh water stream -laid sandstone and shale deposits. Unconsolidated alluvial, terrace, and surficial deposits of Quaternary age overlie the exposed geologic formations in some areas, particularly along larger streams. The permit area lies structurally between the parallel, south-southeast trending Sage Creek and Fish Creek anticlines. The axis of the Sage Creek Anticline is situated about one to two miles west of the western edge of the Yoast permit area. The axis of the Fish Creek Anticline originates near Scotchman's Gulch and extends south -southeasterly dividing the northern first five-year mine block from the neck portion of the permit area. The rock units in the permit area dip predominantly 15 to 20 percent to the north in the north mine block, to the northwest in the neck area, and to the west in the south mine block. More extreme dips of 25 to 35 percent occur locally in the northwest and northeast parts of the north mine block. The rock units are apparently unaffected by any significant faulting within the permit area.