Many first time visitors to Death Valley are surprised it is not covered with a sea of sand. Less than one percent of the desert is covered with dunes, yet the shadowed ripples and stark, graceful curves define "desert" in our imaginations.For dunes to exist there must be a source of sand, prevailing winds to move the sand, and a place for the sand to collect. The eroded canyons and washes provide plenty of sand, the wind seems to always blow (especially in the springtime), but there are only a few areas in the park where the sand is "trapped" by geographic features such as mountains. The biggest "trap" is known as Mesquite Flat Sand Dunes.