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. Highest dunes 130–140 ft (40–43m). Roughly fifteen-square-miles of dunes includes three types of sub-barchan (modified crescent) dunes: crescent, linear, and star shaped. 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.