The Wind River Mountains of west-central Wyoming are bounded on the southwest flank by a thrust fault which dips 20° northeast and has a maximum vertical displacement of 35,000 feet. Seismic data show the magnitude and character of the fault zone. The fault originated from an overturned basement fold which was subsequently broken and thrust toward the southwest. Uplift of the mountains began by folding during the Late Cretaceous, continued throughout the Paleocene, and culminated in thrusting at the end of the Paleocene. Nonmarine sediments in the Green River basin adjacent to the uplift were deposited without interruption in a dominantly quiet-water environment, but as uplift progressed, an increasing number of coarse clastics were derived from the mountain flank. Af er thrusting, early Eocene fluvial sediments from the uplift spread basinward. Gas occurs at Pinedale in tight sandstones of the Paleocene Hoback Formation in a basin facies. Possibilities for both gas and oil exist farther west where cleaner fluvial sandstones interfinger with the basin shales.