Raven Creek field is located on the eastern side of the Powder River basin of Wyoming. Discovered in March 1960, the field has produced more than 10 million bbl of oil. Production is from the "B" sandstone unit of the upper member of the Minnelusa Formation of Pennsylvanian-Permian age. Depth of production is about 8,300 ft (2,530 m). The trap is formed by updip truncation of the "B" sandstone unit against the Opeche Shale at the post-Minnelusa unconformity. Subsurface data indicate that erosion of the productive sandstone was controlled by a resistant dolomite which overlies the "B" sandstone and by the structural configuration at the end of Minnelusa deposition. The trap is on the western flank of a pre-Opeche anticline, the axis of which has been breached by post-Minne usa erosion. Basinward tilting has destroyed the anticlinal closure which probably existed, but has strengthened the stratigraphic closure along the western flank. Data from an experimental seismic survey performed after the field was discovered do not indicate a breached anticline, but do show the area of truncation of the "B" sandstone by an increase in thickness of the Goose Egg-Opeche interval and thinning in the underlying Minnelusa Formation.