Alluvial Fans

Alluvial fans are fan-shaped deposits of water-transported material (alluvium). They typically form at the base of topographic features where there is a marked break in slope. Consequently, alluvial fans tend to be coarse-grained, especially at their mouths. At their edges, however, they can be relatively fine-grained.


Here's another alluvial fan. It's actually two fans that have grown together. Note the numerous channels (light-colored areas)--they mark the locations of the coarsest sediment.

click here to view a coarse-grained alluvial fan deposit.
click here to view a channel deposit in an alluvial fan deposit.

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Some more alluvial fans...
 

Small fan emerging from a wineglass canyon.  Death Valley, CA.

Alluvial fans at fault-bounded western edge of the Black Mountains, Death Valley, CA.

Alluvial fan and center-point irrigation in Dixie Valley, California.

Source: Marli Bryant Miller, Department of Earth Sciences, University Of Oregon, Eugene, Oregon, USA