The Racetrack

Death Valley National Park is filled with many wonders and mysteries.  One of the most notorious is the infamous "Racetrack" playa, where rocks move across the surface of the playa, leaving tracks in their wake.  For years people speculated that it was high winds that moved the rocks around. But, according to an interpretive sign at the parking area, scientists have now figured out how the rocks move.  

With enough rainfall, the playa becomes a shallow lake.  In winter, cold night temperatures freeze the surface of the lake into a sheet of floating ice, embedding the rocks.  The morning sun causes the ice sheets to break up.  Steady breezes catch the floating ice sheets, pushing them along with their embedded rocks.  Eventually the ice melts and the water evaporates, leaving the rocks in new locations until the next event, perhaps years later, moves them again.