Can a heavy stone move by itself, without help from a person? The answer is yes! It looks like magic, but it isn't. And it only happens on the floor of a playa.
A playa is an area of dry, flat land. When it rains, water goes into the playa floor. At night, it gets cold. The top of the water becomes a thin sheet of ice. The ice sheet rests above the water. In the morning, the sun comes out. The ice begins to break. When it breaks, it pushes the stones on the playa floor. They can move five meters in one minute! That means their speed is 0.3 kilometers an hour.
For many years, nobody knew how the stones moved. But in 2014 some people studied the stones carefully. They did their study in Death Valley National Park, California. They used GPS and made a long video of the stones.