Brawley FormationThe Brawley Formation is a geologic formation in the Colorado Desert of Southern California, located in northwestern Imperial County and eastern San Diego County.GeologySandstone and mudstone of the Brawley Formation accumulated between ~1.1 and ~0.6–0.5 Ma in a delta on the margin of an arid Pleistocene lake. It is in the San Jacinto Fault Zone area, including in the San Felipe Hills.FossilsIt preserves fossils from the Pleistocene Epoch of the Quaternary Period, during the Cenozoic Era.