Sailing stone on Racetrack Playa, Death Valley National Park, USA. The inssailing stonesins are large rocks at the end of long tracks of the mud floor of the playa. The stones have long puzzled geologists. Recent research suggests that a water- saturated surface of a thin layer of clay and very strong winds combine to move the rocks, some of which weigh several dozen kilograms. The rocks originate from the steep slopes surrounding the basin.