Natural mystery

(Image credit: Mike Hartmann)In Death Valley's Racetrack Playa, rocks seem to slide across the flat lakebed under their own power. Now, scientists have solved the mystery.

Geologic puzzle

(Image credit: NASA/GSFC/Cynthia Cheung.)The trails are the only evidence the rocks move. Some stretch twice the length of a football field

On the playa

(Image credit: Richard Norris)Biologist Richard Norris stands next to a Racetrack Playa rock trail that may have formed in the late 1990s.

The testing ground

(Image credit: Richard Norris)A boulder brought in to Racetrack Playa to study its sailing stones. Engineer Jim Norris of Interwoof built the custom GPS unit.

Look closely

(Image credit: Jim Norris)The rock on the left side of the photograph is about to move, bulldozed by ice.

There, it moved!

(Image credit: Jim Norris)In this photograph, the small white rock has shifted from the left to the right.

Racing rocks

(Image credit: Jim Norris)Researchers saw rocks sail across Racetrack Playa and set fresh trails, shown here.

On thin ice

(Image credit: Richard Norris)An thin shard of ice from Racetrack Playa's pond, collected Dec. 20, 2013.

Frozen wonder

(Image credit: Mike Hartmann)A GPS-mounted boulder leaves a trail on Racetrack Playa

New tracks

(Image credit: Jim Norris)Parallel trails carved in the wet playa mud.