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Deposition on alluvial fans is caused mainly by decrease in depth and velocity of flow, which results from increase in width as a flow spreads out on a fan. The alluvial-fan deposits of western Fresno County, California, are mudflows, water-laid sediments, and intermediate types. Common voids in the deposits are intergranular openings between grains that are held in place by a clay bond, bubble cavities, interlaminar openings in thinly laminated sediments, and buried, but unfilled, polygonal cracks.
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William B. Bull (1963) studied this question.
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