Oil and gas have been known in non-marine Tertiary rocks in Wyoming since 1896. Commercial oil or gas pools have been discovered in Paleocene and Eocene rocks in the Green River, Washakie, and Wind River basins. The source of most of this oil and gas is believed to be sediments deposited under lacustrine conditions during Paleocene time and again during Eocene time. Oil and gas production from nonmarine beds of latest Cretaceous age is a recent development.

The diastrophic and depositional history from latest Cretaceous through Tertiary time has a significant bearing on essentially all Wyoming oil and gas fields. The Laramide orogeny began with gentle folding in latest Cretaceous time, reached a climax of intense folding and thrust faulting in earliest Eocene time in most parts of Wyoming, and was essentially completed by latest Eocene time. Conventional Wyoming oil and gas fields are those related to structural traps formed during this orogeny.

The Green River, Wind River, and Hanna basins were sites of deposition of more than 20,000 feet of latest Cretaceous, Paleocene, and Eocene strata. Oligocene, Miocene, and Pliocene beds were deposited across the now completely filled basins and high onto the flanks of partly buried mountains. Volcanic debris from centers within or near Wyoming comprises the bulk of these young strata. Regional uplift, large-scale normal faulting, and rapid degradation that exhumed the mountains and re-excavated the basins occurred in late Pliocene and Pleistocene time. During this episode some of the structures containing oil and gas were significantly modified.

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