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Dunes crest is 130–140 ft (40–43m). Primary source of the sand is Cottonwood Mountains to the north and northwest, providing tiny grains of quartz, feldspar and magnetite that form the sand. Roughly fifteen-square-miles of dunes includes three types of sub-barchan (modified crescent) dunes: crescent, linear, and star shaped. Cottonwood Mntns of Panamint Range in background. Death Valley National Monument Est. February 11, 1933. Est. as Death Valley National Park in 1994; 5,270 square miles (13,649 km2). Inyo County, CA.