Though indispensable, rain in the desert knows no moderation.   Capricious and often violent, it brings either too much or too little rain.

More often, freighted with tons of water drawn from moister neighboring areas, these storms loose a brief, localized flood.   Since the water cannot be absorbed by the hard-baked ground, it flows over it in a thin, fast moving sheet, collecting in well-worn channels, or washes down which in roars in huge torrents.   Loaded with mud and debris, the water sweeps out eventually onto the desert flats where it forms short-lived lakes or playas.

Much plant and animal life dies in the brutal lake of these storms, but the destruction is quickly over.

source: A Starker Leopold, The Desert, Time Life Books, Hong Kong, 1980.

Source:http://geology.wr.usgs.gov/wgmt/elnino/enimages/flashfl.JPG