Residents were jolted out of bed Saturday morning when a 4.2-magnitude earthquake struck near Fontana at 5:54 a.m.
4.3-magnitude shake and later downgraded it to a 4.2-magnitude.
Residents in the area said they felt a strong jolt and reported items falling off shelves.
"We felt it very strong. We thought it was an explosion," said Patty Madrid.
The quake struck one mile east, southeast of Fontana, four miles west of Rialto and eight miles east, southeast of Rancho Cucamonga.
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More than 3,700 people in Southern California reported feeling the quake on the USGS' "Did You Feel It?" section.
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Residents 100 miles south reported feeling the quake in San Diego County.
Cal Tech Seismologist Jennifer Andrews said the rattler was about 3 miles deep and shallow, "which can be widely felt." She described the movement as a "strike-slip," meaning the plates moved traversely making the quake feel like a jolt.
Many people quickly took to social media and shared their experiences with the trembler.
"Being a magnitude 4.2 and very shallow, they felt some reasonable shaking," Andrews said.
She added there was a 5 percent chance of a larger earthquake to follow, but the likelihood decreased with time.
Madrid said the earthquake was a very quick jolt and she heard a "loud boom" before going downstairs.
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Another resident said her chandeliers shook on the second-story of her home prompting her to instruct her family to go downstairs immediately.
No injuries or serious damage were reported, according to San Bernardino County Fire Department.
The Los Angeles County Sheriff's Department wanted to remind residents when earthquakes strike to stay indoors until the shaking stops and if you are outside during the shaking to find a clear spot away from buildings and vertical structures, including trees. When driving during earthquakes, pull over to an open location and avoid bridges and ramps.