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The Mystery of Death Valley’s “Sailing Stones” Solved (…again)

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“I love to sail forbidden seas, …
Herman Melville in “Moby Dick” (1851)

Strange tracks cover a muddy plain, located in a remote part of Death Valley National Park, named appropriately Racetrack-Playa. Most of these tracks end behind large boulders of dolostone or syenite, some however start and end without an apparent object nearby. In the first case, it seems reasonable to assume that the rocks moving along the ground formed the furrows – however nobody ever observed the actual process of formation.

The sailing rocks of Death Valley were studied since 1948, when geologists Jim McAllister and Allen Agnew mapped the area and noted the tracks. In March 1952 geologist Thomas Clement tried to observe the rocks moving, but a heavy thunderstorm forced him into his tent. Only the next morning he noted fresh formed tracks on the ground and a thin layer of water covering the ground.  As most of the tracks coincide with the overall wind direction (southwest to northeast), it was assumed that the wind pushed the rocks over the wet and slippery mud. However this hypothesis could explain only a part of the moving rocks, especially the smaller ones. Curiously there is no correlation between the size of the rock and length of the track, even if it seems that larger boulders seem to travel less than smaller ones.

In the following years the strangest ideas tried to explain the mystery of Racetrack-Playa: extraterrestrials, geologists or animals pushing the stones, a hoax to fool tourists, earthquakes, magnetic or gravitational anomalies and unknown wind and water currents.

Geographer George Stanley Druhot (1914-1983) assumed a dominant role of ice, not only as slippery surface, but also as a sort of sail, when ice forms plates around the boulders and increases the surface on which the wind can act.

In 2010 a research team from various institutions (NASA, Slippery Rock University (!)- Pennsylvania, University of Wyoming) reanalyzed the geological and meteorological conditions at Racetrack-Playa, finding evidence to support Stanley´s idea. Geologist Paula Messina showed that the ground is covered by argillaceous sediments and bacterial mats, forming under wet conditions a very slippery surface. The climatic data showed also that ice can in fact form during wintertime in Death Valley, when also most tracks on Racetrack-Playa are formed.  The ice hypothesis (and similar models) explains also the tracks without apparent object nearby, as the chunk of ice melted after the formation of the track, and the deepening of some furrows behind the respective boulder, as the plate of ice surrounding the boulder melts, the rock tends to sink deeper into the mud.

Most researchers agree that a simplistic – one factor assuming – model fails to explain all the sailing rocks. It´s probably the odd combination of mud and bacteria, forming a slippery ground, the topography, forcing the wind into one prevalent direction, the sizes of the boulders, the particular temperature changes experienced in Death Valley and the occasional formation of ice, that like a ghostly hand moves the rocks around the desert.


MILLER, M.B. (2005): Geological landscapes of the Death Valley region. Earth-Science Review 73:17-30

David Bressan About the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts through time. Follow on Twitter @David_Bressan.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Llewellin 1:28 am 07/23/2013

    like Eddie replied I’m blown away that a mother can profit $7573 in 4 weeks on the computer. did you see this web site ……

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  2. 2. AtlantaTerry 3:30 pm 07/25/2013

    Why doesn’t anyone do time-lapse photography of the rocks?

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  3. 3. EyesWideOpen 3:43 pm 07/25/2013

    The last hypothesis in the article for the moving rocks is in the year 2010, when it was solved three years ago. The “solved again” part of the article title is a mystery. Is there a new hypothesis?

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  4. 4. jgrosay 4:30 pm 07/25/2013

    I’d add a bit to this right explanation of how stones move, and it seems the phenomenon is not restricted to areas where freezing temperatures may exist, but even in hot places. There’s a kind of soil named ‘expansive clays’ that do change in volume according to its water content, architects know about this, as it add difficulties in the foundations of new buildings. Water content in the atmosphere may change from day to night, as nights are colder, and the relative humidity of air is expected to raise during nights; if the humidity of clays changes along, and part of the soil dilates in a different way to other, an slope may appear on which stones can slip, even more if a thin layer of mud is on the surface, acting as a lubricating agent to facilitate that the stones move. However, even when it’s sure that stones move, in the absence of human or animal presences, stones photographed one day appear in a different place some hours after, and it leave tracks, nobody has ever actually seen stones moving, and natives say stones are moved by the spirits of sorcerers, shamans or wizards who behaved unproperly in life, and are confined inside the stones as a punishment. Natives tell the visitors that they better never pass a night close to the area of moving stones, and it’s good trusting those having lived in a place for centuries; when people in Venezuela forgot that natives lived on the sides of hills, and not in the valleys, and started building towns in the plains, they suffered huge human and economical losses after a heavy rain flooded the valleys, destroying everything in its path. If they’ve asked themselves the reason why natives never lived in valleys, modern Venezuelans would have avoided many casualties. Another habitude of people that lived in South America before the Catholic kings send away Christopher Columbus, habitude that is also forgotten today, is that when a town was destroyed by an earthquake, they never rebuilt the town, they left the ruins, and built a new town elsewhere.

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