Southern California Regional Rocks and Roads

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In the San Diego area, there aren’t too many earthquakes. That doesn’t mean there aren’t many faults. Some of the larger structural faults in Southern California pass through San Diego County. All the faults listed on this page are capable of a M7.0 or greater.

The San Andreas Fault passes close by the eastern end of the county in the Imperial Valley, ending near Bombay Beach near the northeast corner of the Salton Sea. A southern extension of the San Andreas Fault, known as the Imperial Fault, has had some major earthquakes that have been felt here in San Diego. Two in particular, 1940 and 1979, were responsible for a fair amount of slip which was visible in agricultural fields and highways in the area.

Offset concrete slabs under asphalt on old US 80 near Holtville. — Offset concrete slabs under asphalt on old US 80 near Holtville between James Road and Bowker Road.

More than a foot of offset is visible here. The perpendicular cracks are from the concrete paving underneath the asphalt.

Cracking as a result of the various earthquakes along the Imperial Fault.

Rails of the Holtville Interurban bent at the Imperial Fault crossing. These tracks have since been removed.

The San Jacinto Fault makes its pass through the area via Anza, Borrego Springs, and Ocotillo. It is more active than its parent, the San Andreas. Sometimes these earthquakes are large enough to be felt here in the San Diego area. Large canyons, hills, and other features created by the fault are quite visible in the desert climate in the Anza-Borrego Desert State Park area.

Fault controlled valley along Gilman Springs Road just south of Jackrabbit Trail near Hemet, CA.

The Elsinore Fault is the next closest fault to San Diego. It passes through the Lake Elsinore area before heading below Palomar Mountain, Julian, and Banner Canyon. Various features, such as linear canyons and springs alignments can be seen along this fault.

Elsinore Fault lineament as it passes by Lake Henshaw and distant Volcan Mountain from Palomar Mountain.

The closest major fault to San Diego itself is the Rose Canyon-Newport-Inglewood Fault. Its last major event was in 1933 in the Long Beach area. Locally, it hasn’t ruptured in a few hundred years. There is still conjecture about when the next event will be and how large. As such, it isn’t as apparent as faults like the San Andreas. This fault stays mostly offshore in San Diego County, coming onshore at La Jolla Shores. Rose Canyon, its namesake, follows the fault line from SR-52 south to Pacific Beach. From there, the Rose Canyon Fault roughly follows I-5 to downtown San Diego, where it steps over to San Diego Bay roughly along Park Blvd. While fault activity is less frequent than some of the other major faults in the region, it is still a source of concern for the area. Large earthquakes, in the M7.0 range, can and will eventually occur along this fault. As it runs through a very populated portion of the city, any activity along it can have devastating affects. Studies have been done in the past by the USGS and the CGS to determine what those affects may be and are available through their websites for purchase.