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1 Western Slope Carbon, Inc. <br />December 15, 1981 <br />Page 5 <br />' and test data reflect subsurface conditions at widely spaced points, <br />variation in subsurface conditions from those encountered in our borings <br />' should be anticipated. <br />i <br />GEOLOGY <br />' Available geologic mapping (Hail, W.J. Jr., 1972, U.S.G.S.)* indicates that <br />the Pit No. 6 area is entirely underlain by the upper Cretaceous Mancos shale <br />' formation. (See Figures 2, 3A, and 3B, Geologic Time Scale, Regional Geologic <br />Map and Key). The Mancos shale is characterized as consisting of dark brown <br />to gray, non-resistant, clay-shale. In the Hotchkiss vicinity, a sandy cal- <br />careous shale and calcareous sandstone layer is occasionally identifiable <br />' within the Mancos shale. This layer, termed the Juana Lopez member, is <br />roughly 300 to 350 feet above the base of the formation. Based on the <br />structural projections of Hail, the thickness of the Mancos shale beneath <br />the Pit No. 6 area is likely to be somewhat over 400 feet. <br />' As observed in the borings, the Mancos shale consists of a gray-brown to <br />gray, poorly indurated, silty shale or siltstone. It is occasionally slightly <br />sandy and is indistinctly bedded. Veins and stringers of calcium carbonate <br />are relatively common. The residual soils overlying the shale vary in thick- <br />' Hess from about three feet to thirteen feet and consists of medium stiff to <br />very stiff clayey to sandy silt with a varying percentage of shale fragments. <br />' Weathering tends to be deeper in the gently sloping Swale areas than on the <br />side slopes. <br />' The Mancos shale is underlain in this area by the lower Cretaceous Dakota <br />sandstone which has a maximum thickness of about 150 feet. The Dakota sand- <br />' stone consists of light gray to brown, strongly indurated, resistant, quartzose <br />sandstone which locally contains some dark gray carbonaceous shale, and con- <br />glomerate layers. Where it crops out some five miles to the southwest, it <br />forms steep slopes and prominent cliffs. <br />' *Hail, W.J. Jr., 1972, Reconnaissance Geologic Map of the Hotchkiss area, <br />Delta and Montrose Counties, U.S. Geological Survey Miscellaneous Geologic <br />' Investigations Map, I-698. - <br />