The shallow quake hit at 8:41 a.m. and was centered in the Mayacmas Mountains about 27 miles north-northwest of Santa Rosa, the USGS said.
Measured at a depth of less than mile, the temblor's epicenter was some 90 miles north of San Francisco and about 5.6 miles west-northwest of The Geysers.
The earthquake was felt throughout Sonoma and Napa counties, ABC7 sister station KGO reported.
It was not immediately known if anyone was injured or any damage occurred.
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