A desert is dangerous. Water in the desert is rare. But in the rare instances where there comes too much water in the desert?
This is on highway Highway 395 at Dunmovin, California, near Death Valley. See that semi?
According to the all-knowing Wikipedia, a mudslide is 50% silt/sand/clay/junk and at least 30% water (and 20% houses, trees, small animals?). Especially in a desert, when flash flooding occurs, there isn’t any vegetation to keep the sand in place and so it all gets swept up and carried away by the water.
That particular mudslide occurred an intense period of flash flooding in the Mojave Desert this last August (2010). The Guzzler has a few articles written about that time (you have to scroll down, though. It’s a bit of a pain).