The Mysterious Moving Rocks Of Racetrack Playa

These rocks are intriguing because they move, leaving tell-
tale trails in the clay. Since the 1940's researchers have
documented the trails. This happens at several playa in California
and Nevada. There's no record of anybody seeing one of the
rocks move, and scientists aren't quite sure how it happens. But
they know that it's not the work of animals, gravity, or earthquakes.