'Sailing Stones'

Saw this photo today in a link from boston.com and was definitely unaware of the phenomena of 'sailing stones.' Admittedly, I didn't do any significant research here, but looking in wikipedia, it seems at this point there still isn't a sure answer to why the stones move on their own. Below is a brief description and a couple of theories ripped right off the wikipedia page:

The sailing stones (sliding rocks, moving rocks) are a geological phenomenon where rocks move in long tracks along a smooth valley floor without human or animal intervention. They have been recorded and studied in a number of places around Racetrack Playa, Death Valley, where the number and length of travel grooves are notable. The force behind their movement is not understood and is subject to research.

Most hypotheses favored by interested geologists posit that strong winds when the mud is wet are at least in part responsible. Some stones weigh as much as a human, which some researchers, such as geologist George M. Stanley, who published a paper on the topic in 1955, feel is too heavy for the area's wind to move. They maintain that ice sheets around the stones either help to catch the wind or move in ice floes.