The San Rafael Swell is a large geologic feature located in south-central Utah, USA about 30 miles (50 km) west of Green River, Utah. The San Rafael Swell, approximately 75 miles (121 km) by 40 miles (64 km), 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.