The San Rafael Reef is a geologic feature located in Emery County in central Utah, part of the Colorado Plateau. Approximately 75 miles (120 km) long, it is the name given to the distinctive eastern edge of the San Rafael Swell. Composed primarily of steeply tilted layers of Navajo and Wingate Sandstone, it has been eroded into tall fins, domes, cliffs, and deep canyons.The San Rafael River, Interstate 70, and Muddy Creek all cut through the San Rafael Reef.