Measured at a depth of 1.86 miles, the 4:08 a.m. quake was centered just south of Ontario International Airport, according to the U.S. Geological Survey. The agency initially recorded the temblor as a 3.5.
There were no reports of injuries or damage.
ABC7 viewers said they felt the earthquake in Chino Hills, Rancho Cucamonga and Upland.
"That sucker shook hard! Here in Mira Loma," Loretta Romero wrote on Facebook.
A magnitude 2.7 aftershock struck the area at 5:33 a.m. and was later downgraded to a 2.5, the USGS said.