The author with one of the rocks (Photo: Richard Saunders)
If you're familiar with the American Southwest or even if you're a fan of the paranormal, you've heard of the mysterious stones that move across the surface of a dry lakebed in Death Valley called Racetrack Playa. Hundreds and hundreds of rocks, scattered about the surface of this several square mile mudflat, have left trails behind them where they've moved across the surface. Nobody has ever seen one move, despite many studies. I came as close as anyone could.
Proposed explanations run the gamut from natural to paranormal to alien. Strange magnetic forces, psychic energy, alien spacecraft, teenage pranksters, and even transdimensional vortices have all been proposed. The leading scientific hypothesis is that the rocks are moved by high winds, on rare occasions when the playa is wet enough to be extremely slippery, and conditions are just right. I've always had trouble with this explanation. I used to play in mud flats as a kid, and when a rock is glued onto that surface it's pretty damn hard to move. The rocks at Racetrack Playa are quite streamlined, and it's hard to imagine any wind strong enough to break their bond with the surface and shove them along deep enough to leave those trails. The real cause of the moving rocks, it turns out, carries a lot more punch than wind, and requires conditions that are not oddball and that are easily observable.
In the early spring of 2002, I made one of my many trips to Racetrack Playa with two friends, Dan Bocek and John Countryman. The surrounding mountains were still covered with snow, and the playa itself was firm but had a large lake covering about a fifth of its surface, perhaps an inch or two deep at its edges, concentrated at the playa's south end where it's lowest. We ventured out, armed with cameras, shortly before sunrise. The temperature was just above freezing. The wind, from the south, was quite stiff and very cold. When we reached the lake, we found to our great surprise that the entire lake was moving with the wind, at a speed we estimated at about one half of a mile per hour. The sun was on the lake by now and we could see a few very thin ice sheets that were now dissolving back into water. This whole procession was washing past many of the famous rocks. It's easy to imagine that if it were only few degrees colder when we were there — as it probably had been a couple of hours earlier — the whole surface would be great sheets of thin ice. Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor. Certainly a lot more horsepower than wind alone, as has been proposed. The wind was gusty and moved around some, and since the surface is not perfectly flat and with rocks and various obstructions, the water didn't flow straight; rather it swapped around as it moved generally forward. Ice sheets driven by the water would move in the same way, accounting for the turns and curves found in many of the rock trails.
But don't take my word for any of this. I told you we had cameras, and I captured the event on video. It's well worth two minutes of your time:
That nobody has ever seen the rocks move is easy to believe. When there's water on the surface of the playa, you're not allowed to go out there — and indeed, you probably wouldn't want to. Thus there's nobody around when the ice sheets drag the rocks.
We missed the actual event, probably by a couple of weeks, so we didn't get the first real video of a moving rock. No doubt someone soon will. But we did see and document all the forces at play, and I think our explanation is far more plausible than any previous hypotheses.
Update: My hypothesis was finally confirmed in 2014 by a team who beat me to the punch. Read about it here!