ABSTRACT

The south front of the Owl Creek Range of Central Wyoming has about 5 miles of structural relief with respect to the Wind River Basin at the south. In the past this structural relief has been interpreted as the result of great low-angle thrusting of the range over the adjacent basin. Additional work in the critical frontal zone reveals an interrelated complex of many fault types resulting from stress reorientations in rocks of differing strengths at differing structural levels. Structural classes include: (1) broad frontal arching of the brittle basement complex to produce lines of keystone graben along the axes of opposite direction of tilting, (2) a frontal uplift zone consisting in part of moderately dipping reverse faults which are largely buried under basin fill, (3) gravity slide masses moving off the steep range flanks to over-ride and partially camouflage the true frontal structures. These slide structures of brittle Paleozoic carbonates glided on weak Cambrian shales at locations where frontal faulting has undermined their lower supports by juxtaposition of weak Cambrian and weak Triassic formations and where keystone graben faulting had separated and freed their upper slopes. In the past, these masses of Paleozoic rocks resting on Triassic were regarded as true frontal structures providing the best evidence for the theoretical, great sub-Owl Creek thrust. With the superficial nature of these slides recognized, the fundamental uplift structures in poor surface exposures seem to be moderately dipping thrust or reverse faults.

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