The Green River Formation of Wyoming is a thick lens of sedimentary rocks which was deposited in a large playa-like complex. These sediments accumulated in three major depositional environments: (1) marginal (siliciclastic sandstone and siltstone); (2) mudflat (marlstone); and (3) lacustrine (oil shale, trona, fossiliferous limestone). In general, the basinward transition of lithofacies is from coarse-grained, cross-bedded, channel sandstones at the basin margins to algal and oolitic limestones to clastic and algal dolomitic marlstones and finally to oil shale and trona at the center of the basin. The lateral intertonguing of these lithofacies and the repetition of large- and small-scale lithologic cycles provide a basis for the reconstruction of the physical, chemical, a d biologic evolution of Eocene Lake Gosiute.

Thin, but extensive, algal marlstone units reflect the basinward migration of Lake Gosiute's shoreline during periods of increased aridity. Widespread fossiliferous limestones suggest transgressive shoreline conditions. The occurrence of thin, extensive tuff beds establishes time-stratigraphic relations among the lithofacies. The correct interpretation of lithofacies changes in a closed basin can be an important tool for locating deposits of rich oil shale, trona, and perhaps oil- and gas-bearing channel sandstone reservoirs similar to those now being developed in the Uinta basin.

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