Cottonwood Wash Road follows the trace of the Cockscomb, the northern end of the East Kaibab monocline, the structure that defines the eastern side of the Grand Canyon. A monocline is a type of fold in which one side of a fault at depth has risen, slicing through the rocks below, but not breaking through the overlying sedimentary layers, rather like a rug draped over a stairstep. At Grand Canyon, the East Kaibab monocline has formed the Kaibab Plateau, which the Colorado River had to slice through to form the deep gorge we see today at the national park. Along the Cockscomb, there is no Grand Canyon, but erosion has exposed the heart of the monocline and the Jurassic-Cretaceous sediments that it displaced.
At the lower end, the rocks look...kind of wrong. The towers of Navajo sandstone lack their normal "beehive" appearance, and instead look kind of spiky (upper center in the picture below). At this point they have been stretched and deformed, and somewhat broken up by the folding process. I wondered if slope stability was a problem where rocks have been messed up in this fashion (more on that in a second).
hiking guide for the Paria Canyon region (2010) mentions a side canyon at the upper end of the Narrows that is easily explored. Not anymore...look below to see how it looked last week. No vegetation on it at all except a little patch of grass at the base. I can't find any information about the rockfall and would appreciate some additional info if anyone out there knows about when it happened.
Come on our trip! Or, check out these resources:
Some technical details about the East Kaibab Monocline in Grand Staircase-Escalante National Monument: http://www.utahgeology.org/pub28_pdf_files/Tindall.pdf
A detailed road guide to the geology of the Cottonwood Wash road: http://www.utahgeology.org/road_logs/uga-29_first_edition/NM_guide/gsenmlog.pdf