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Geology Report Grassy Creek Coal Mine The published source for the basic geology, the regional strati- graphic column and coal sequences, the nomenclature and rock descriptions is "Geology and Mineral Fuels of Parts of Routt and Moffat Counties, Colo- rado, U.S.G.S. Bulletin 1027-D, by Bass, Ebv and Campbell, 1955." Additional information was taken from the private source: Coal Resources of the Long and Teiken Properties for Energy Fuels Corporation by Saunders Associates Inc. Data was also gathered in the field and from drill hole logs. Stratigraphy: Rocks exposed in the Grassy Creek Mine Permit Area are part of a se- quence of beds called the Iles Formation. The Iles with the conformable overlying Williams Fork Formation makes up the Cretaceous Mesaverde group. The Iles rests conformably on the Cretaceous Mancos shale, which does not • crop out in the mine area. The Iles Formation is a sequence of rocks about 1,500 feet thick. For the purposes of. this report we have broken the Iles into fouz map units. The lowermost is designated Kil on the Geology Map and is the bottom 600 feet. The Tow Creek sandstone, although not exposed in the mine area, is the basal unit of the Iles Formation. It is a massive, cliff forming light brown sandstone, finegrained, well sorted, tightly cemented and slightly calcareous. It is about 100 feet thick. The next major sand- stone is the "double ledge forming" light gray and white sandstone occurring about 400 feet or more above the base of the Iles. It usually forms two prominent ledges. The No. 1 coal zone represents the basal coal zone of the lower coal group and occurs just above the "double ledge forming" sandstone. A coal zone has been encountered at this level in some of the deeper drill holes. The interval between these two sandstones consists of beds of light-brown, light-gray, and white sandstones interbedded with gray sandy shale. Kil rocks aze exposed in the southeast portion of the permit azea. The top of this map unit is between the No. 1 and No. 2 coals of the Lower Coal group. The next map unit in ascending order is shown on the Geology Map as Kit; it includes rocks between No. 1 and No. 3 coals which enclose the No. II.D-2