At least 12 aftershocks were reported in the hour after, most under 2.5 magnitudes.
There are reports of damage around Ukiah and Willits.
Photos from Willits resident Renee Morgan show damage in her home.
There are also about 5,000 people without power in Willits, according to the PG&E outage map.
Governor Gavin Newsom's office says the governor has been briefed on the quake and they are coordinating with emergency officials to assess impacts and damage.
The 5.6 quake measured at a depth of around 5 miles. The deeper an earthquake is, the less shaking is felt.
USGS scientist discusses 5.6 earthquake that hit Mendocino County
MAP: Significant San Francisco Bay Area fault lines and strong earthquakes
Zoom in on the map below and compare where you live to the significant faults and where strong earthquakes have struck in the Bay Area.
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