There are large stones on the dry desert ground of a playa, or dry lakebed, of Death Valley, California. These stones move in long tracks along the smooth valley floor without human or animal intervention. They have been studied for years by scientists, with no clear findings.
Are you sure people or animals aren't moving them?
Based on the shape of the trails behind the rock, it seems like they move at times when the lakebed is muddy. Since there are no other disturbances to the lakebed floor, it seems unlikey that animals or people are responsible for the movement.
Also, some of these rocks weigh several tons, making it impossible to move them without heavy equipment.
What about the wind?
Maybe. The winds that blow across the lakebed travel from southwest to northeast. Most of the rock trails are parallel to this direction. This strongly suggests that wind is the prime mover or at least involved with the motion of the rocks.
Strong wind gusts are thought to nudge the rocks into motion. Once the rock begins to move it doesn't take as much effort to keep it going, so a much smaller wind can keep it moving. Curves in the rock trails are explained by shifts in wind direction or in how the wind interacts with an irregularly shaped rock.
What about ice?
One idea is that water freezes around the rocks and then wind, blowing across the top of the ice, drags the ice sheet with and the rock across the surface of the lakebed. Some researchers have found highly similar trails on multiple rocks that strongly support this theory. However, the transport of a large ice sheet attached to the rock might be expected to mark the lakebed surface in other ways - these marks have not been found.