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.
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