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Exposed here are three distinct layers - clues to ancient landscapes. #1 Moab member of Curtis Formation (youngest layer). Deposited as dunes on a beach, this light-colored sandstone has almost completely eroded away here. Look for it at Delicate Arch and high in the Fiery Furnace. #2 Slickrock member of Entrada Formation (middle layer). This fine-grained, cliff-forming sandstone dominates the park. Once a vast desert, slickrock is the major arch-forming layer of the park. #3 Dewey Bridge member of Carmel Formation (oldest layer). This muddy-looking, reddish brown layer is the lumpy and contorted remains of a tidal flat environment. Softer than the layers above, it erodes faster - an important factor in arch formation.