In a remote corner of Death Valley National Park lies a dried lakebed called the Racetrack Playa, home to one of nature's most perplexing mysteries: hundreds of rocks that move across the desert floor on their own, leaving long trails behind them without any human or animal intervention.
Some of these "sailing stones" weigh up to 700 pounds yet somehow travel hundreds of yards, sometimes changing direction or even moving in perfect parallel with neighboring rocks. The phenomenon puzzled scientists for nearly a century, with theories ranging from magnetic fields to alien intervention.
The mystery was finally solved in 2014 when researchers captured the movement on camera. During rare winter conditions, when the playa fills with just the right amount of water and overnight temperatures drop below freezing, thin sheets of ice form around the rocks. When morning sun causes the ice to break up and light winds push the ice sheets, the rocks are carried along with them—creating an eerie geological ballet visible only through the trails left behind once the water evaporates.