UC Riverside

The San Antonio Canyon is within the eastern San Gabriel Mountains, southern California. The steep slopes of the canyon contain mostly fractured Mesozoic plutonic and Paleozoic and Precambrian metamorphic rocks. The San Andreas fault, San Jacinto fault, and the Sierra Madre-Cucamonga fault are all capable of producing large earthquakes with strong ground shaking and all bound the eastern San Gabriel Mountains near the San Antonio Canyon. There are five main rock avalanche deposits within the canyon which have been interpreted previously to be between 100 ka and 2.6 Ma. Preliminary dates suggest these rock avalanche deposits are several magnitudes younger than previously thought. This makes the canyon a very active and dynamic landscape with large landslide and earthquakes hazards more prevalent than previously expected.