County, Utah. This feature is a large northeast trending upwarp approximately long and wide that is part of a much larger, double-plunging anticline (e.g., dome) structure. This large, regional fold exposes rocks of Pennsylvanian through Cretaceous age. Resistant beds of sandstone are exposed as hogbacks on the steeply upturned east and west flanks of the anticline and are referred to locally as "reefs." Three perennial rivers (the Muddy, San Rafael, and Price) flow eastward across the San Rafael Swell into the Green and Colorado River systems. See also Canyonlands National Park References Colorado Plateau Physiographic sections Regions of Utah Regions of Arizona