Rock Slide

Natural History, April, 1999 by Judy Rice

Treated to less than five inches of rain a year, lakes in eastern California's Death Valley often look like dry floors made of millions of small sunbaked tiles. In these realms, pattern and geometry, rather than unruly biology, dominate. But even in such an inanimate landscape, nature can leave tracks.

Dozens of rocks--craggy lumps of dolomite weighing up to seven hundred pounds--are in the process of trekking across one of the take beds, now known as the Racetrack. Although their curious trails have been known for decades, no one has ever actually caught the rocks in the act (their progress is most likely both slow and intermittent, or the result of lithic stealth). One long-favored theory held that at the rare times when the surface is muddy and suck, wind moves the rocks. But in 1995, John Reid Jr. and his colleagues from Hampshire College in Massachusetts calculated frictional forces and concluded that a more likely explanation involved ice. A cold night after a rain would create a thin ice field on which the rocks could ride in a strong wind. This could also account for the similar paths of neighboring rocks.

Photographer William Neill managed to give his basketball-sized, lifeless subjects an eerie presence by capturing a momentary glow and texture imparted by the last moment of sunlight on a winter day.