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^~ ~ <br /> <br />~, <br />2.7.1.2 Stratigraphy <br />Bedrock in the Craig area is comprised of Cretaceous and Tertiary sedi- <br />mentary formations underlain by an ancient igneous and metamorphic base- <br />ment complex. Table 2.7-1 summarizes the Stratigraphy in the mine plan and <br />adjacent areas. <br />The youngest material in the general area is Quaternary alluvial material <br />associated with the Yampa and Williams Fork Rivers and some smaller trib- <br />utaries (Figure 2.7-2, Simplified Geologic Map of the Trapper Mine Area). <br />Other formations present, youngest to oldest, are the Lewis Shale, the <br />Williams Fork formation, the Iles formation, and the Mancos Sliale. <br />The Mancos Shale, a 4000 foot thick sequence of dark grey marine shales, <br />lies far (2000 ft) beneath the mine. Above the Mancos Shale lies the Iles <br />formation. It is comprised mainly of sandstones with some shale beds. The -' <br />upper-most member of the Iles formation is the Trout Creek sandstone. This <br />cliff-forming quartzose sandstone is a widely used marker unit. Above the <br />Iles formation lies the Williams Fork formation. Figure 2.7-3 shows a <br />generalized cross section of this formation through the Trapper Mine. <br />2-349 <br />