The Wilkins Peak Member of the Green River Formation is a nonmarine, closed-basin, dolomitic carbonate deposit that intertongues with siliciclastic deposits at the basin edges. A transect from the basin margin to the basin center reveals six major subfacies. (1) The alluvial-fan subfacies is poorly sorted boulder conglomerates, cross-bedded gravels, and horizontally laminated grits and sands. These are interpreted, respectively, as fan-apex incised channels; mid-fan channel-bar deposits; and fan-toe, shallow, braided channels. (2) Sand-flat subfacies consists of wedge-shaped sheets of dolomitic sands extending tens of kilometers into the basin center and changing from "Bouma-like" graded units (20 to 30 cm thick) near the basin edge to horizontally laminated or coarse gra ed beds (1 to 10 cm thick) toward the basin center. These are interpreted as having been deposited by decelerating sheetfloods. (3) Dry-mud-flat subfacies includes densely mud-cracked and graded dolomitic mudstone laminites and thin beds. These are interpreted as subaerial mud flats in which sheetflooding and in-basin, shallow debris flows were the important depositing mechanisms. (4) Nonsaline-ephemeral-lake subfacies is dolomitic mudstones with laminations composed of pinch-and-swell sand, a thick mud cap, and sparse deep mud cracks. These are interpreted as sporadically exposed, shallow-lake margins or isolated shallow ponds. (5) Perennial-lake subfacies is oil shales or finely laminated dolomitic mudstones that are rarely cracked. These are interpreted as having been deposited in a s allow but persistent lake. (6) Saline-ephemeral-lake subfacies consists of either dolomitic mudstones and oil shales disrupted by intrasediment salt-crystal molds, or massive trona and/or halite beds containing mud partings. These are interpreted as brine-soaked lake and mud-flat deposits, or deposits in very shallow brine pools.

These subfacies occur as asymmetric cyclic sequences 3 to 4 m thick that are interpreted as random sheetflood deposits superimposed on transgressive and regressive beds laid down in a shallow central lake which occasionally dried up. The small-scale lacustrine cyclic sequences probably provide delicate indications of minor climatic changes. These sequences not only provide a facies model for other deposits but also a possible criterion for predicting the large-scale geometry of less well-exposed basins.

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