Coconino Cross Bedding
March 27, 2003
This image taken along the Bright Angel Trail in the Grand Canyon clearly shows cross bedding in the Coconino Sandstone layer exposed by the canyon. The tan colored Coconino Sandstone is one of the most dominant features of the Grand Canyon. This erosion resistant layer forms a spectacular cliff of 300-500 feet (90–150 meters) not far below the Canyon’s rim. Dating to approximately 260 million years ago, the Coconino is composed of nearly pure quartz sand. The cross-bedded features indicate that the Coconino Sandstone is basically petrified sand dunes. Formed through aeolian (wind) deposition, sand dunes slowly migrate downwind. Sand grains are carried up the windward side of the dune then deposited near the peak. Angled layers are formed as the newly deposited sand avalanches down the leeward side of the dune. The strata of the Coconino Sandstone show some of the most distinct examples of cross-bedding on the planet.