Do you see how the sediment that is collecting at the bottom of the California mountains in (A) looks like a fan from above? This is called an alluvial fan! Alluvial fans form when sediment eroded from mountains is deposited on a valley floor like in (A). The rocks that are formed from an alluvial fan have large pieces of sediment that are not very round like the sediment in (B).
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Courtesy of Martin Miller, University of Oregon and Earth Science World Imagebank
Last modified January 6, 2004 by Lisa Gardiner.
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