I've never been to this place, and don't know a thing about the physics of it all. But, I do have experience with this type of soil when it gets wet. In the Badlands of South Dakota, the clay soil isn't just slippery - it's almost slimey! When it's damp, it sticks to shoes and you eventually end up walking on platform soles. But, when water puddles on the soil, the real fun begins. We never tried to skid a big rock across it, but I wish someone there would try. It might be hard to reproduce the same conditions as at the Playa - so, it sounds like a job for the Mythbusters!