The quake hit at around 9:29 a.m. It had a depth of 10.8 km, the USGS said.
USGS initially reported it as a 4.6-magnitude earthquake before downgrading it minutes later to a 4.1, before updating it to a 4.2 later in the day.
A ShakeAlert was sent to Northern California residents about the quake.
There is no word of any injuries or damage.
This comes a day before the Annual Great ShakeOut, where emergency systems will be tested for earthquake preparedness. As a part of this, MyShake app users will get an earthquake test alert on Thursday.
This is also one day after the 34th anniversary of the devastating 1989 Loma Prieta earthquake.
Click here for the latest stories and videos about earthquakes here in the Bay Area and around the world, and click here for more information on disaster preparedness.
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