For years in the Racetrak Playa of Death Valley National Park, stones large and small have been drifting across the dried surface, leaving muddy trails behind. Until now, the cause for their independent movement has been unknown.
Death Valley is the hottest, driest and lowest land in North America, eliminating most theories of what could cause these stones to move - sliding in mud, a slant in the ground, and so on.
Last year, two researchers from the Scripps Institution of Oceanography at University of California San Diego decided to test a few theories by attaching GPS devices on some of the stones, and waiting patiently. In just one day, the researchers witnessed 60 rocks move across the ground.
What they discovered is that the thin ice that trapped the rocks during winter melted in the midday sun, and then the ice, water and rocks were blown in the wind, making it seem as if the stones moved by themselves.
Check out this Nat Geo video about the sailing rocks.