TERTIARY FAULTS WITH REVERSED MOVEMENTS NEAR COPPER MOUNTAIN, CENTRAL WYOMING

brian and younger rocks which moved upward and southward during very early Eocene time on a moderately high angle thrust fault. Subsequently the leading edge or toe of the thrust was extensively broken by normal faulting, and the part of the thrust block north of the toe rose and became the arch known as Copper Mountain. ed toe area is the Cedar Ridge fault scarp which is composed of post-thrust arkoses of the Lower Eocene Wind River Formation. Cedar Ridge is directly underlain by mudstone and muddy conglomerate of the Middle and Upper Eocene Tepee Trail Formations. However, within this central region there are horst blocks of Wind River Formation and the Steffen Hill complex of Paleozoic strata and Precambrian ig-neous and metamorphic rocks. Drill hole data suggest that arkose of the Wind River Formation exists in small outcrops and more extensively in subsurface a short distance north of the Cedar Ridge fault. ingly, detrital glauconite occurs in this arkose. In most of the toe which was drilled, how-ever, the Tepee Trail is not underlain by the Wind River Formation but by Paleozoic and Pre-cambrian rocks, indicating extensive erosion of Wind River sediment on the toe of the thrust prior to Tepee Trail time. It is postulated that the Wind River horst blocks, and very pos-sibly the Steffen Hill complex as well, were grabens at the time of this erosion and were The eastern Owl Creek Mountains of central Wyoming are part of a block of Precam-The southernmost visible structure in the fault-Most of the area of the toe between Copper Mountain an