The Pacific Ocean temblor, which was centered 102 miles west of Capetown, California, hit at 8:39 a.m. at a depth of 3 miles, according to USGS.
There were no immediate reports of damage or injuries.
The Ferndale Enterprise reported on Twitter the rolling quake was felt in Ferndale, a city in Humboldt County that has many well-preserved Victorian homes.
The quake comes hours after a magnitude-4.0 earthquake struck the Trabuco Canyon area. That quake struck at 2:09 a.m. about 8.1 miles northeast of Trabuco Canyon and 14.9 miles south-southwest of Riverside.
People reported feeling the shaking across Los Angeles, Orange and Riverside counties.
The Associated Press contributed to this report.