Mormon Rocks was formed by the folding of rock along the San Andreas Fault between the North American and Pacific tectonic plates. It is composed of cemented sedimentary rock like conglomerate and displays pockmarks on its surfaces caused by thermal expansion and erosion. The North Etiwanda Preserve protects rare Riversidian sage scrub habitat and endangered species. It was impacted by a 2003 wildfire but the vegetation has resiliently recovered, though ongoing threats from pollution and development loom.