Next time you happen to pass Death Valley, visit Racetrack Playa and see the famous and mystifying “sailing stones.” As you can see by the photo above, the stones leave plain tracks in the dried-out mud of the playa. (“Playa” is a dried-up lake or pond that sometimes fills when it rains. We had a nice one right next to our high school football field.)
What makes the stones “sail”? Well, no one has observed it happening, but time-lapse photography in 2014 suggested the stones were powered by a delicate balance of ice, water, and wind. A thin layer of ice sticks to the bottom of the stones–some of which weigh several hundred pounds–and when a stiff wind comes up, off they go. That’s the theory, anyway.
There’s also a theory that space aliens may be responsible. UFOs traverse the incalculable vastness of interstellar space to come here and push rocks around. I don’t think much of that theory.