Strangers in a Strange Land" because most humans are strangers here, and it seems like almost everything about this landscape is truly strange. One of those strange landscapes are playa surfaces. I previously talked about the Death Valley salt pan, one aspect of an interior drainage desert, but there are many other "lakes" in the park which never collected much in the way of salt. They have smaller drainage basins, and no river systems fed into them, so the most common mineral on the floor of these playas is fine-grained clay. They will occasionally have water following flash flood events, but most of the time they are dry, and the clay breaks up into millions of small, mostly hexagonal mudcracks.
So, how is it that they move? If you are looking for a definitive answer, I am sorry, I don't actually know. No one truly does, because no one has ever seen it happen. I think we can safely dismiss stories of aliens playing jokes, elves, and pixies, and of strange magnetic forces. The stones lie on exceedingly flat surfaces, so gravity sliding is probably not involved. It seems that only one force exists in the Death Valley region that can account for the movement of these rocks: the wind.
There may be another important factor. The playas where the rocks move are at higher elevations where freezing temperatures are common. If enough rain has fallen, water may cover the playas and freeze around stones sitting on the playa surface. It is suggested that broken sheets of ice around the stones can act as sails, helping push the rocks along. This idea is supported by rock trails that move in tandem, as if the rocks were physically connected. This explanation works for me, but additional testing of some of the rocks shows that ice cannot completely explain the movement (researchers put stakes around some stones, and they moved out, passing through spaces barely bigger than the stones themselves).
So the moving stones are still a bit of a mystery. One of these times, someone is going to brave a horrific windstorm and will be standing there with a camera when the stones are moving about. At that time we will be able to see the elves themselves pushing the rocks along!
gigapan 360 degree view of the playa (click on the image below to see how gigapans work; it's pretty amazing). More gigapans of Racetrack and other parts of Death Valley can be found here: http://www.gigapan.com/gigapans?gallery_id=7940&order=most_popular&page=2&per_page=10
A final note: if you visit Racetrack or any of the other moving stone sites, please leave the stones alone. They are mysterious, but not mystical. They are normal run-of-the-mill rocks with no unusual properties other than being on a playa, and the position of each stone is recorded with GPS. Stealing the rocks (and that is what you would be doing) will screw up years of research. You will also take from the enjoyment from other visitors.