Sierra Madre Fault Zone ( also known as the Sierra Madre-Cucamonga Fault ) runs along the southern edge of the San Gabriel Mountains for a total of , where the northwesternmost comprises the San Fernando Fault ( the section responsible for the 1971 San Fernando earthquake ) . A 1980s paleoseismic study that included a trench investigation and mapping revealed that a major earthquake had most likely not occurred to the east of the San Fernando rupture area for at least the last several thousand , and possibly the last 11,000 years
1971 San Fernando earthquake
1971 San Fernando earthquake
Sierra Madre Fault Zone