Laserfiche WebLink
northwestern Colorado. This member is afine-grained, well-cemented, cliff-forming <br /> unit. The sandstone is generally white and commonly has a thickness of 100 feet or <br /> more. Outcrop exposures of the Trout Creek Sandstone Member often exhibit joints <br /> that form polygons a foot or more in diameter. <br /> The Williams Fork Formation is a sequence of sandstone, shale, and coal beds <br /> that comprise the upper half of the Mesaverde Group. The total thickness of the <br /> formation ranges from 1100 to 2000 feet increasing in a westerly direction. In the <br /> Edna Mine Area, the formation varies from about 1,300 To over 1,500 feet thick. In <br /> the vicinity of the Foidel Creek EMRIA site about 10 miles west of the study area, <br /> the formation is divided into four members by Ryer, (1977). These members are <br /> named, in ascending order: lower-coal bearing member, marine shale member, <br /> Twentymile Sandstone member and the upper member. <br /> The lower coal-bearing member is composed chiefly of siltstone and shale with <br /> thin sandstone and coal beds of the "middle group". Bituminous coals in the middle <br /> group include, in ascending order: the Wolf Creek, Wadge, and Lennox coal beds <br /> (Bass, et ol, 1955). Because sandstone and siltstone beds of the lower coal-bearing <br /> member are resistant to erosion, the entire member forms moderately resistant dip <br /> slopes above the Trout Creek Sandstone. This geomorphic feature is observed at the <br />• Edna Mine, the Energy Fuels Corporation's strip mine near the confluence of Foidel <br /> and Middle Creeks, and at the Energy Fuel's Strip Mine IJo. I, located south of Foidel <br /> Creek in the southwestern part of TSN, R86W. <br /> The marine shale member is composed of both fissile and nonfissile, dark grey <br /> shale with occasional beds of grey siltstone and sandstone. This member is poorly <br /> exposed, but is easily identified from drill cuttings and geophysical logs from <br /> boreholes in the Fish Creek and Trout Creek mine areas. Based on these borehole <br /> logs, the average thickness of the marine shale member is about 600 feet. <br /> The Twentymile Sandstone member is composed of light grey, fine-grained, <br /> well-cemented sandstone that ranges from 100 to 250 feet Thick in the region. This <br /> ledge-forming sandstone splays into several separate beds of sandstone west of the <br /> study area (Bass, eT al, 1955). Borehole data collected in this study from the Fish <br /> Creek Mine indicates this member ranges from 146 to 240 feet Thick. <br /> The upper member of The Williams Fork Formation is a sequence of sand, <br /> shale, and coal beds that conformably overlie the Twentymile sandstone. Near The <br /> Fish Creek Mine the upper member is approximately 200 feet thick. West of the Tow <br /> Creek Anticline the upper unit is reported to be 850 feet thick. The member <br /> includes the Fish Creek coal bed and local sandstone beds that resemble the <br /> Twentymile Sandstone (Bass, et al., 1955). <br /> <br />Revised 7-81 <br />2.5-45 <br />