In Death Valley's Racetrack Playa, rocks seem to slide across the flat lakebed under their own power. Now, scientists have solved the mystery.
The trails are the only evidence the rocks move. Some stretch twice the length of a football field
On the playa
Biologist Richard Norris stands next to a Racetrack Playa rock trail that may have formed in the late 1990s.
The testing ground
A boulder brought in to Racetrack Playa to study its sailing stones. Engineer Jim Norris of Interwoof built the custom GPS unit.
The rock on the left side of the photograph is about to move, bulldozed by ice.
There, it moved!
In this photograph, the small white rock has shifted from the left to the right.
Researchers saw rocks sail across Racetrack Playa and set fresh trails, shown here.
On thin ice
An thin shard of ice from Racetrack Playa's pond, collected Dec. 20, 2013.
A GPS-mounted boulder leaves a trail on Racetrack Playa
Parallel trails carved in the wet playa mud.