Alluvial Fans

The Copper Harbor Conglomerate is made up of alluvial fans. This hypothesis was proposed by Douglas Elmore in 1984. Many people have debated it and most support it. We make hypotheses like this to help us understand the conditions of formation of this remarkable rock formation.  There are some mind stretching implications: 1.  It implies a mountain on one side.  Where is that mountain now?  2. It suggests desert conditions.


Brockway Fan is 10 km wide. Extending from Copper Harbor to Agate Harbor

This Alluvial fan near Stovepipe wells in Death Valley CA is 9.5 km wide

One way to test the idea of an alluvial fan is its scale.  Is the Brockway Conglomerate outcrop shaped like a real alluvial fan? We checked its width--almost the same as one fan we found on Google Earth from Death Valley--one place you can find many such fans. 

The Brockway fan makes a ridge because the conglomerate of the fan is much harder than the sandstones and shales that make up the other rocks surrrounding.  So they erode more rapidly. and make lowlands.

It is also possible to test the thickness of the fan which should be greatest in the center and should thin toward the edges.  This also seems to be true for the Brockway fan.  What are some other ways to test?

Debris flow deposits on an alluvial fan in Panamint Valley at the base of Panamint Butte in the Cottonwood Mountains in Death Valley National Park (Inyo County). Note how the stream channel is incised near the top of the fan, but the debris flow deposit is spread out on the lower fan surface.