2020-08-21_GENERAL DOCUMENTS - C1994082

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A and 7,980 feet at the summits of ridges within the southeastern portion of the permit area. Slopes range from 1° in Scotchman's Gulch to 100' at isolated sandstone bluffs. The terrain is characterized by broad west and northeast facing moderately sloping benches and ridges that are deeply incised, and barren, brush covered, southwestward facing cliffs where more resistant sandstone outcrops exist. The long, sloping landforms of these areas roughly coincide with the strike and dip of the underlying bedrock. The permit area is dissected by several small, ephemeral drainages which flow into two principal stream systems: Sage Creek on the southwest and Grassy Creek on the southeast. A detailed discussion of the Yoast Mine surface water system is presented in Tabs 7 and 16 of the permit application package (PAP). 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 mined comprised 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. 5