The raging water picks up any loose material in its path. The faster the water moves, the larger the pieces of rock it picks up. Badwater alluvial fan. Photo from NPS archives. Dumping debris Eventually the rock-laden torrent reaches the narrow canyon mouth.
Water rushes out of the canyon into the open valley.
Without the constricting force of the canyon walls, the racing flood water slows down dramatically, loses energy, begins to drop its sediment load, and breaks into several small streams. The largest rocks drop out first, and the smallest sediment is carried farthest from the canyon mouth. Only the finest silts and clays are carried all the way to the bottom of Death Valley. Each flood deposits an new batch of sediment. In areas with higher rainfall, running streams would remove this dumped debris, but in dry Death Valley, much of it stays put.