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i ~F. Geology - Nature, depth and thickness of the ore body: The geology of the Callahan Trust/D.A. Shale property has been investigated from the viewpoint of using that property as the in-situ test site for the Occidental Oil Shale process. The Callahan Trust/D.A. Shale area is located in Garfield County, Colorado, between DeBeque and Grand Valley in the southern part of the Piceance Basin. The oil shale described in the following section on stratigraphy outcrops along the Roan Cliffs on the north side of the Colorado River. Mt. Callahan is in the eastern part of the area with an elevation of 8606 feet and is almost 3600 feet above the river. Riley Gulch and Logan Wash, the two major drainages of the area, range in depth below the ridges from several hundred feet to al- most 3000 feet. However the ridge tops are as much as a quarter mile wide, and travel by four-wheel drive vehicle across the area is not difficult once the top of the ridges has been reached. Stratigraphic units outcropping in the Logan Wash area include the Wasatch formation of Eocene age, the Green River formation, also of Eocene age, and basalt of late Tertiary age. The Wasatch formation does not outcrop on the property. However, it must be crossed by every access road reaching the area from any direction except north. The Wasatch formation is of continental origin and comprises silt- stones with a high percentage of clay and sandstones. It underlies the oil shale formation throughout the basin. The main oil shale section is contained in the Green River formation which is comprised of three units, the Douglas Creek member, the Garden Gulch member, and the Parachute Creek member containing the oil shale, and overlain by the sands of the Uinta formation. The Douglas Creek member is formed of cross-bedded ripple-marked sandstone with some limestone and shale. It forms a prominent outcrop in Logan Wash. The Garden Gulch member overlies the Douglas Creek member and underlies the Parachute Creek member. The predominant rock type is papery shale. Barren marlstone is also common along with some oolitic algal limestone and very minor oil shale. The Garden Gulch member forms prominent gray sloping outcrops that can be confused with the overlying Parachute Creek member from a distance. The principal difference between the two members is the lack of carbonate in the Garden Gulch member compared with the Parachute Creek member which is predominantly carbonate. The Parachute Creek member is comprised of shale and marlstone and is the oil shale producing unit in the Piceance Basin. Donnell (1961) divides the Para-. chute Creek member into three zones; the upper oil shale zone, a middle barren zone, and a "middle and lower oil shale zones" comprising, in essence, a lower zone. The highest grade oil shale is in the "Mahogany Ledge" in the lower part of the upper high-grade zone, and is approximately 90 ft. thick. It is underlain by about 100 feet of medium-grade oil shale and overlain by about 100 feet of medium-grade oil shale.