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rock fan
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rock fan

geology
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History

rock fan, fan-shaped bedrock surface at the foot of a mountain, often where a stream flows out onto a piedmont slope. It is often covered with a thin veneer of alluvium and may be confused with an alluvial fan. Rock fans are usually quite steep (20° to 26° slope). It has been suggested that they represent the early stage of pediment development. See pediment.