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0937 that the total thickness of the Green River Formation within the Piceance 9reek basin varies in relationship to the basin depositional axis. At its maximum, this formation exceeds 3,000 feet in thickness. " Within the Green River Formation, all member contacts are gradational and represent transgressive-regressive sequences or changes in the mineralogic composition of the rocks. The Green River/Uinta Formation contact is conformable and is characterized by a complex intertonguing relationship. North of NOSR 1 and 3, six northward extending tongues of' Green River Formation have been identified. These include the Yellow Creek, Dry Fork, Thirteen Mile Creek, and Black Sulfur Tongues identified by Duncan and others (1974); the Coughs Creek Tongue identified by O'Sullivan (1975); and the Stewart Gulch Tongue identified by Hail (1977). Field work for this hydrologic investigation noted the presence of tongues on NOSR 1. In addition, a photogeologic evaluation for potential geologic hazards on NOSR 1 (1980) identified multiple tongues of the Green River Formation. However, neither the field work nor the photogeologic evaluation identified and mapped indiv~dual tongues. The sedimentary structures, the mineralogy, and the fossil content of the formation, as detailed by Bradley (1931) and Stransfield and others (1951), indicate that this formation was deposited in a Middle Eocene lacustrine environment. 3.5.1.2.1 Douglas Creek Member The Douglas Creek Member is conformable over and intertongues with sediments of the Wasatch Formation. It consists mainly of light- to medium-brown, cross-bedded, and ripple~marked sandstone, with lesser amounts of limestone and gray shale. The Douglas, Creek Member is characterized by its drab colors and resistance to erosion. It represents the beginnin9 transgressive phase of Lake Uinta, and forms a clastic wedge which thins basinward from the Douglas Creek Arch. Its areal extent roughly coincides with the original lake bed of Lake Uinta (Ritzma, 1965; Sladek, 1974; McDonald, 1978). The type section of the Douglas Creek Member (Bradley, 1931) is located at the head of Trail Creek near Douglas Pass, in T5S, R102W. It crops out around the southern and western sides of the basin, where it is 400 to 800 feet thick. East of Parachute Creek it grades into the Anvil 3-9