So there are apparently things called Sailing Stones, also called Sliding Rocks or Moving Rocks.  But basically it refers to a phenomenon where rocks move along smooth valley floors without human or animal interaction… and no one knows how or why they do it.  But they know they do it because they leave grooves and tracks behind them as they move!

Well, after I read the article, that’s a half truth.  There is a good theory, it’s just not proven.  Basically, some scientists marked several large rocks positions and monitored them.  If any of them moved, it was after winter, so they are pretty sure winter is involved.  Since they are in flat valleys, they are pretty sure stream-line winds are involved.  So the theory basically goes that wind in these flat areas is intensified through some type of icy phenomenon, and these rocks catch blasts of 90+ MPH wind gusts… when they start to slide, it doesn’t take as much sustained wind to keep them moving… like a train that takes a lot of power to start, but not so much to keep moving.

You can read more on the wiki.