<p>The rocks are famous because they move, leaving tell-tale trails in the clay, like this one. This happens at several playa in California and Nevada. There's no record of anybody seeing one of the rocks move, and scientists aren't quite sure how it happens. But they know that it's not the work of animals, gravity, or earthquakes.
</p><p>Photo credit: NASA/GSFC/Cynthia Cheung
</p><p>To read a feature story on the Racetrack Playa go to: <a rel="nofollow" class="external text" href="http://www.nasa.gov/topics/earth/features/roving-rocks.html">www.nasa.gov/topics/earth/features/roving-rocks.html</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/gsfc/4882084749/">Mysterious Roving Rocks of Racetrack Playa</a>