Sailing stones are stones that can be found on the ground in Death Valley, California. The stones in question appear to have slided several metres across the ground, leaving behind a long grooved trail in the sand, with no signs of any human or animal intervention whatsoever. Differently shaped stones leave differently shaped trails, and some even appear to have turned over in mid-travel, changing the groove as they go. There have also been accounts of several stones starting next to each other and moving in a parallel trail, but with one of them abruptly changing its course to the left or right or even back in the direction it came from. Most tracks develop over the course of several years, and most stones only move every two or three years.
This geological phenomenon has been the subject of many theories, ranging from scientific to paranormal. The generally accepted theory is that the stones move due to heavy gusts of wind in combination with several conditions that make it easier for the stones to leave such long trails. The surface has to be saturated but not flooded, there has to be a thin layer of clay on the ground, and the wind has to sustain a strong momentum over a period of time. The gusts of wind in this area can reach a speed of up to 140 kilometres an hour in winter storms, and stones of less than a few inches high are susceptible to them. Researchers have also discovered that small rafts of ice are formed under the stones at freezing temperatures, reducing the friction and making the stones more buoyant. Despite these explanations, the rocks have never been observed as they migrate, as this would demand exceptional patience as well as luck.
The paranormal explanations for this phenomenon range from magnetic forces and psychic energy to alien spacecraft and transdimensional vortices.