The Racetrack is a really gorgeous playa (dried up lakebed) at an elevation of 1131 feet in the Panamint Range in the west of Death Valley. People will love to tell you that the rocks on the playa move mysteriously by themselves. There are trails of hundreds, even thousands of feet long left behind by the rocks. While there's no absolutely proven scientific explanation, it's pretty widely believed that the wind pushes the rocks along under the right conditions: after it rains, the surface of the playa (which is very much like clay) becomes extremely slick and slippery.
Click the USGS link above for some cool photos and a more detailed explanation.