When the Rocky Mountain chain began to rise, some 70 million years ago, the crust to its west was stretched, producing a mosaic of ridges and broad basins. Drainage into the basins created large inland lakes, including the Green River Lakes of the Utah-Colorado-Wyoming Tristate and Claron Lake of southwest Utah. All of these lakes gradually filled with sediments of the Paleocene and Eocene Periods (60-50 million years ago); the deposits in the Green River Lakes would eventually yield the famous oil-shales of the Roan Plateau while deposits in Claron Lake would become prized more for their natural beauty.
Compacting into layers of limestone, dolomite, siltstone and conglomerates and capped by volcanic tuff from the Oligocene Period (30 million years ago), the Claron Formation was lifted with the rest of the Colorado Plateau during the Miocene-Pliocene Uplift, some 25-10 million years ago. Erosion and faulting would eventually expose the Claron beds along the edge of regional plateaus; Cedar Breaks National Monument, a spectacular natural amphitheater on the west edge of the Markagunt Plateau and Bryce Canyon National Park, on the east edge of the Paunsaugunt Plateau, protect the most scenic exposures.
Rich in iron oxides and manganese oxides, the colorful limestones and dolomites have eroded into striking rock formations, known as hoodoos. These pinnacles, capped by more resistant rock layers have been split apart by stream erosion and freeze-thaw fracturing. Once lying beneath an ancient lake, they now gleam in the bright Utah sun and adorn calendars across the globe.
