Caltech says the 3.9-magnitude earthquake was centered about six miles south-southwest of Yucaipa and hit at 7:44 a.m. It was earlier reported that the earthquake was a magnitude 4.2.
Joe Berdecia, a clerk at a 7-Eleven on Yucaipa Boulevard, said he thought the shaking was just a large truck driving by the store.
There were no reports of injuries or damage. ABC7 viewers reported feeling the earthquake in Yucaipa, Redlands, Moreno Valley, Fontana, Lake Elsinore and Riverside.
Cody Cox of Yucaipa said the earthquake was the first for his 3-year-old son.
"We heard it, and then my son got all scared," he said. "He came running to me, and picked him up, and told him it was fine."
James Rich in Riverside said it was his first time feeling an earthquake, too.
"It felt like the fat guy next door fell over," Rich said.