For almost a century, scientists were stumped as to how the rocks were able to move, proposing everything from aliens to really, really strong breezes, but with the development of new technology they've started to narrow in on a solid hypothesis.
The stones were first discovered in the early 1900s, and people were immediately mystified. The rocks, which range in size from about six to 18 inches in diameter, don't travel in straight lines- they can veer left and right and even move backwards. Stones of equal size didn't travel equal distances, and to top it all off, no one had ever actually witnessed the stones moving.
In fact, each rock generally only moves once every three years, and travels for about ten seconds before stopping. Even with modern equipment, the odds of catching a rock in the act aren't great.
A 2011 study proposed the theory that ice floes form around the rocks in certain, very specific conditions, and help the stones slide along the ground when it's muddy and slippery with rain, guided by gusts of wind.
A study released in 2013 further bolstered the ice sheet idea by proposing that the narrowing trails left behind the rocks could be related to the lessening amounts of water available in the valley.
Also in 2013, several of the stones were reported stolen, which is pretty upsetting, considering some of the rocks were named by researchers. I'm so sorry, Karen, Nancy and Mary Ann.
If you think Death Valley National Park's sailing stones are crazy, check out the awesomeness that Yellowstone National Park has to offer.