alluvial fan
"The surface of an alluvial fan is like a segment of a cone. The radial profile toward the lower reach is concave and the cross-sectional profile is convex. A delta ..."
"An alluvial fan is like a delta on top of the ground. It's like a dog wagging its tail. It could be over here and then move over there for a while. You can see it over there, but not necessarily here until flooding and then it changes its course and goes out into a fan shape into the valley," he said. "For archeology, it's great because we need the sediments to cover up campsites and things like that."
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