Sunday's shaker occurred shortly before midnight PDT and was centered outside King City, about 160 miles south-southeast of Sacramento, the U.S. Geological Survey said.
There were no reports of damage or injury in the rural area.
The USGS said the quake occurred along California's famed San Andreas Fault, which triggered the famed 1906 San Francisco Earthquake and the Loma Prieta quake in Oct. 17, 1989, which killed 64 people and caused significant damage in the San Francisco Bay Area.
Seismologists said the fault in the King City area has been largely a mystery. "The fault in this region is locked, exhibiting no creep at the surface and generating very few microearthquakes that are associated with minor slipping at depth," the USGS said.
California held its annual statewide series of earthquake drills Oct. 18. Students learned about earthquake science and safety and practiced diving under their desks in preparation for a genuine shaker.