There were no immediate reports of damage, but the temblor was followed by dozens of small aftershocks.
According to the USGS, the quake was felt across a wide swath of the region, from the Inland Empire west to Los Angeles and Orange County. Two minutes later, a magnitude-3.2 quake was recorded in the same area, which is more than 100 miles northeast of downtown San Diego. Its epicenter was six miles south-southeast of Mount San Gorgonio and eight miles north of Cabazon.
Some nearby residents reported via social media that the shaking of their homes woke them up. More than 6,700 people had reported feeling it by 5:30 a.m. on the official USGS website.
Veteran seismologist Lucy Jones tweeted that the quake occurred near a complex part of the San Andreas fault that can not be clearly seen on the surface there because it is covered by another fault. "It was a very good rumble", she said.
On Twitter, users from across the region reported experiencing the latest spate of temblors.
In Los Angeles County, there were no reports of damage or injuries, Los Angeles County Fire Department Supervisor Rangel said.