The Mesquite Sand Dunes are at the northern end of the valley floor and are nearly surrounded by mountains on all sides. Due to their easy access from the road and the overall proximity of Death Valley to Hollywood, these dunes have been used to film sand dune scenes for several movies including films in the Star Wars series. The largest dune is called Star Dune and is relatively stable and stationary because it is at a point where the various winds that shape the dunes converge. The depth of the sand at its crest is 130-140 feet (40-43 m) but this is small compared to other dunes in the area that have sand depths of up to 600-700 feet (180-210 m) deep. Star Dune is shaped like a starfish. The primary source of the dune sands is probably the Cottonwood Mountains which lie to the north and northwest. The tiny grains of quartz and feldspar that form the sinuous sculptures that make up this dune field began as much larger pieces of solid rock.