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. Highest dunes 130–140 ft (40–43m). Grapevine Mountains 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.