Ancient debris flow deposits, Anza Borrego State Park, San Diego County, California

Ancient debris flood and debris flow deposits exposed in the canyon walls in Fish Creek Wash exposed Split Mountain in Anza Borrego State Park (eastern San Diego County). The "fanglomerate" beds, consisting of sandstone and conglomerate beds formed from sediments deposited on an alluvial fan on the margin of the Salton Trough in the early stages of its formation in Late Miocene time (between 15 and 5 million years ago). Each of the conglomerate beds represents a debris flow or flood event. The entire sequence shown in this sequence probably represents several dozen major storm events that occurred within a period of several thousands of years. Minor storm events are probably poorly represented or not preserved in the sequence.

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