The temblor struck at 1:04 a.m. at a depth of 0.6 mile with a magnitude of 5.2, according to the USGS.
A quake of such strength can generate considerable damage, but there were no immediate reports of injuries or damage in San Diego or Riverside counties, although the earthquake triggered a minor rockslide on Montezuma Valley Road, about 14 miles southeast of Borrego Springs. California Highway Patrol officers were on the scene clearing the area, the CHP reported.
The quake's epicenter was 13 miles north-northwest of Borrego Springs in San Diego County and 16 miles south-southwest of La Quinta in Riverside County. It was strong enough to be felt in the city of Los Angeles, as well as in San Bernardino and Orange counties and in parts of Mexico.
The earthquake occurred along the San Jacinto Fault, historically the most active fault in Southern California, according to seismologist Lucy Jones. It was near a magnitude-6 earthquake in 1937 and a magnitude-5.3 earthquake in 1980, Jones reported.
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“We have never seen a San Andreas earthquake triggered by a San Jacinto earthquake,'' Jones wrote on Twitter, referring to the state's most famous fault, the one along which the so-called “big one'' is expected to hit someday.
“Every earthquake has a 5 percent of triggering an aftershock that is bigger than itself -- always within a few miles of location of the first earthquake,'' Jones wrote.
There were at least eight aftershocks in the same general area within 3 hours and 10 minutes. The strongest were magnitude-3.5 shakers at 1:06 a.m., 1:33 a.m. and 4.14 a.m. -- all at a depth of slightly more than 6 miles.
The quakes did not raise the risk of a tsunami, according to the USGS.
Actress McKaley Miller, who was raised in Texas, tweeted in response to the main quake, “I literally thought a ghost was pushing my bed, but thanks to Twitter, I now know it was just an earthquake... I've never been so scared.''