In almost perfectly flat dry lakebed at the upper end of Death Valley there some strange rocks known as 'sailing stones' are dotted about the otherwise almost smooth lake bed, some of them weigh up to 36kg, but behind them are tracks sometimes tens of metres long as if they were moving. The tracks can be straight or zig zagged and some of the stones have been marked and their positions seem to change relative to stakes put in the ground, but noone has ever seen a stone move.
Ralph Lorenz, a scientist at Johns Hopkins University has come up with a new explantion, a neat combination of both. The lake floods a couple of inches deep, and as it does so a small ice berg forms around the stone, the water level increases slightly and beacuse ice floats this gives the stone lift, reducing the friction with the ground. The high winds are then able to push the stones along forming the long tracks. They have done some exeriments which support their hypothesis, though it will be hard to know what is happening for sure until someone actually sees one moving.
Having been to racetrack lake (playa) and seen the tracks, they seem to defy explanation. Some of the tracks are hundreds of meters long, others only a few meters. All different sizes and shapes of rocks "sail" across the playa. And RD is right, the tracks do cross each other. one other thing, the wind does blow there, ferociously at times. The wind has always blown when I've been in Death Valley (mostly in winter months), sometimes so forcibly that it's hard to stand. As my partner once said, as a gust almost sent our truck into the ditch, "The wind doesn't blow here, it sucks"