This area is home to the Fransiscan Assemblage of rocks. These mangled, misshapen, motley group of metamorphosed sedimentary rocks were once part of the accretionary wedge that built up at the bottom of a subduction zone. Tectonic forces bent, folded, cooked, smeared, and finally lifted these rocks, exposing their inherent weaknesses to the erosive power of water. The relatively random nature of these weaknesses results in a pretty random-looking erosional pattern.

Below are a few examples from the SW U.S. of what erosion does to uplifted units that contain regular and ordered weaknesses: