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-4- <br />is papery shale. Barren marlstone is also common along with <br />some oolitic algal limestone and very minor oil shale. The <br />Garden Gulch member forms prominent gray sloping outcrops that <br />can be confused faith the overlying Parachute Creek member from <br />a distance. The principal difference between the two members <br />is the lack of carbonate in the Garden Gulch member compared <br />with the Parachute Creek member which is predominantly carbonate. <br />The Parachute Creek member is comprised of shale and marlstone <br />and is the oil shale producing unit in the Piceance Basin. <br />Donnell (1961) divides the Parachute Creek member into three <br />zones; the upper oil shale zone, a middle barren zone, and a <br />"middle and lower oil shale zones" comprising, in essence, a lower <br />zone. <br />The highest grade oil shale is in the "P7ahogany Ledge" in the <br />lower part of the upper high-grade zone, and is approximately <br />90 ft. thick. It is underlain by about 100 feet of medium-grade <br />oil shale and overlain by about 100 feet of medium-grade oil <br />shale. <br />The Unita formation overlies the Parachute Creek member and <br />is comprised of sandstones and some barren marls tones and is <br />recognized in the D.A. Shale area as the caps of the highest <br />hills. A fine-grained basalt flow rock, an erosional remnant <br />of the extensive flows that cover Battlement and Grand t4esas <br />south of the Colorado River, occurs on Mt. Callahan in the eastern <br />part of the D. A. Shale area but covers only a few acres. <br />