These are the Mesquite Flat Dunes near Stovepipe Wells in Death Valley National Park. This photo was taken from the top of the highest dune looking northeast towards the rest of the dunes. The eastern part of Mesquite Dunes is the best place to go for photography since those dunes don't get as many footprints from visitors.
Canon EOS 5D Mark II, f/5.6 @ 300 mm, 1/125, ISO 100, No Flash