POTD June 26, 2013: San Rafael Swell, Sevier County, Utah

San Rafael Swell, Sevier County
Photographer: Robert F. Biek

Alluvial and wind-blown sediment partly conceals the Jurassic-age Entrada Sandstone in the Last Chance Desert, which occupies the axis of the Last Chance anticline. The narrow, jagged, black ridge at the center of the photo is a basaltic dike of probable late Tertiary age (3 to 5 million years old) that intrudes the Entrada Sandstone.