On a seemingly ordinary day, the residents of San Bernardino County were jolted awake by an unexpected event - a 4.2-magnitude earthquake. The tremor, though relatively minor in comparison to some of the more devastating quakes that have struck California in the past, served as a reminder of the ever-present threat of seismic activity in this region.
San Bernardino County, situated on the San Andreas Fault line, has long been susceptible to earthquakes due to its proximity to tectonic plate boundaries. As such, it is no stranger to seismic events. However, this recent quake serves as a stark reminder that even seemingly dormant fault lines can awaken at any moment.
San Fernando Valley, Riverside, San Bernardino and portions of Orange County.
The quake was centered near where the San Andreas and San Jacinto earthquake faults come together.
The area was the site of a magnitude-5.2 earthquake in 1970. The main quake came 20 minutes after a magnitude-4.1 foreshock. The shaking knocked a radio station off the air and triggered mudslides and rockfalls that blocked roads.
Michael Guardado, who works at the front desk of the San Bernardino National Forest's Lytle Creek Ranger Station, said after Friday's quake the “building shook hard" and he had heard that “a lot of rocks” had fallen onto Lytle Creek Road.
Lytle Creek, said she felt “a hard boom and a shake.”
“It wasn’t very long, but it was scary,” she told The Associated Press.
USGS provides information about earthquakes by state and preparedness information, including helpful information for those in California.
While Dr. Jones said that the earthquake itself is not necessarily a cause for concern, she did say that Friday's quake is a good opportunity to talk with your loved ones about your natural disaster preparedness plan. 
"It's people helping each other that get us through the big disasters," said Jones.
Most of Los Angeles felt light shaking, while the epicenter of the quake experienced strong shaking, USGS reported.
The quake came days after the region experienced similar temblor on Monday morning around 12 miles south of Rancho Palos Verdes, according to USGS. The earlier quake originated in the ocean and was felt over a large part of Southern California, including Santa Barbara, San Bernardino, and San Diego.
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