Alluvial fans at Mormon Point, Death Valley National Park, Inyo County, California

Alluvial fan at Mormon Point in Death Valley National Park (Inyo County). The small size of the alluvial fan relative to the large canyons in the Black Mountains is because the east side of southern Death Valley is sinking relative to the west side of the valley. In addition, glacial Lake Manly filled Death Valley during the Ice Ages of the Pleistocene Epoch. Waves and currents in Lake Manly redistributed sediments throughout the lake basin area. At its maximum extent, the lake was about 800 feet deep. Shoreline terraces associated with the lake's shoreline are visible near the center-right in this image. The lake finally dried up about 9,000 years ago, and the modern alluvial fans on the east side of Death Valley have accumulated since that time. Note the narrow character of the lower canyon near its mouth but that the valley broadens upstream. This landscape characteristic is called an "hour-glass canyon". This landscape morphology forms as the headwater region of the drainage expands over time, yet the lower stream channel is confined to an ever-deepening canyon. As a result, when a rainstorm occurs across the headwaters region, the runoff of this larger upland region is concentrated in the canyon "bottleneck" near the canyon mouth. This is where the most hazardous conditions exist during and following a desert storms and is the site where debris flow or debris floods have their greatest impact.

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