Tracking the rolling stones of Racetrack Playa

It's the time of year when the sailing stones of Racetrack Playa in California's Death Valley are on the move. Probably. No one has actually seen these huge rocks move along the flat, dry lake bed. But, we know they do. Sometime, when no one's looking, usually after freezing weather or heavy wind or rain, the rocks up and scoot themselves leaving unmistakable travel grooves in their wake. Extremely patient scientists studying the wanderliths have concluded that wetter winter weather plays a role in the stone rolling, but they're still not exactly sure how it all works. Take a look at these slow-motion stones below.

The sailing rocks are not small. Many are about the size of a loaf of bread and weigh upwards of 25 lbs.

The dry lake bed that is Racetrack Playa is pancake flat. It's 4 1/2 miles long but only rises one inch along that entire length.

Trails as long as 1,500 feet have been found. What's even more puzzling is sometimes you can follow these trails and there's no rock at the end of it. Image by NASA

Rain, ice, and strong winds likely work together in getting the rocks on the move. Rock movement is more evident after stormy winters.

Sometimes the rocks, like the one above, will travel along and just run themselves into the ground. Image by NASA

Rock trails will overlap, cross, travel in parallel, make wide curves, sharp turns, and zigzags. Image by NASA

Timelapse video is likely the only way we'll get to actually see the rocks in motion. The exposure time would be tricky as sometimes the rocks don't move for years. 

The rocks are ordinary dolomite that tumbled out from the surrounding mountains. Their mobility is more due to their location than their composition