Debris flows are a major process of sediment transport to the Colorado River from ungaged tributaries in Grand Canyon National Park, Arizona. Debris flows are slurries of clay to boulder-sized particles of large magnitude and short duration that occur infrequently. They are the source for potential large volumes of sand for beaches on the Colorado River. Debris flows create and maintain hydraulic controls (rapids) on the Colorado River at tributary mouths. (See also W89-09240) (Author 's abstract)