In Death Valley National Park , you won't find much moving across the Racetrack Playa, a dry lakebed about three miles long and 1 1/2 miles wide. Well, except rocks. The playa, about 30 miles southwest of Scotty's Castle Visitor Center, is known for its mysterious moving rocks. No one has actually seen them move, and no one is certain about how they move, though the tracks they leave behind indicate that they do wander. Some theories attribute their movement to rain and wind. Some point to ice. A few things about the rocks are clear. They eroded from nearby mountains and most are a few pounds, though some weigh hundreds. The surface they rest on is also unusually flat, varying only about an inch from one end to the other.