The earthquake hit at 9:56 a.m. and was centered 13 miles east-southeast of Anza in Riverside County. The area is prone to seismic activity.
It was initially reported as a 5.2-magnitude quake, but it was later downgraded to 4.7. Caltech seismologist Kate Hutton said the confusion with the magnitude was due to their computer software.
"We always are refining our software, but we're definitely going to have to work on that one," she said.
Hutton said the quake was felt from the San Diego area all the way up to Los Angeles County. Harriet Eckstein of Palm Desert said the temblor rattled the windows of her shop.
"It really shook, shook the building, and then all of a sudden, it just went into a rolling motion," she said. "I've been through a lot of earthquakes, but I'm still shaking inside."
About 45 minutes after the initial earthquake, there were at least 55 aftershocks, Caltech said.
"The whole house cracked, and then it just started to sway," Belinda Lyons of Beaumont described. "I kind of froze, so I was just waiting to see if it got worse."
Residents gathered at the Sunshine Market in Anza to exchange stories about rattled nerves. But it was its owner who was left the most shaken. Gerpreet Singh says she was filling up a customer's propane tank when she felt the Earth move. She said she ran because she thought the propane tank might blow up.
For firefighters in nearby Pinon Pines, the protocol called for pulling their fire trucks out of the station.
"We came outside, we could see small landslides, dust coming up out of canyons," said firefighter Richard Rice.
And while there were no reports of any serious damage, firefighters helped clear Highway 74 of fallen rocks.