The San Rafael Swell is a large geologic feature located in south-central Utah about 30mi west of Green River, Utah. The San Rafael Swell, approximately 75by, consists of a giant dome-shaped anticline of sandstone, shale, and limestone that was pushed up during the Paleocene Laramide Orogeny 60-40 million years ago. Since that time, infrequent but powerful flash floods have eroded the sedimentary rocks into numerous valleys, canyons, gorges, mesas and buttes. The swell is part of the Colorado Plateau physiographic region.GeographyInterstate 70 divides the Swell into northern and southern sections, and provides the only paved road access to the region. The swell lies entirely within Emery County.The northern Swell is drained mainly by the San Rafael River, while the southern Swell is drained mainly by Muddy Creek which eventually joins the Fremont River to become Dirty Devil River northeast of Hanksville, Utah. The Dirty Devil River flows southward into the Colorado River, while the San Rafael River joins the Green River before it also flows into the Colorado. Muddy Creek cuts into the western edge of the Swell, exits at Muddy Creek Gorge, and then flows across the Blue Hills Badlands near Caineville to its confluence with the Fremont River.
