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(NEWSER) –  California Gov. Jerry Brown has declared a state of emergency after a magnitude 6.0 earthquake rolled through the San Francisco area early today, reports the LA Times, in the biggest temblor to hit the region since 1989.  It was initially reported at 6.0, and later revised upward.

The California Highway Patrol's Golden Gate division tweeted that it's checking bridges and other structures for "obvious signs of structural integrity;" it later said that preliminary reports "are looking positive," while noting widespread power outages.

PHOTOS: Earthquake Rattles Napa Valley

It was "just a rolling sensation," one witness tells the San Francisco Chronicle. "It felt like I was on a boat in the bay." At least 70 people have been sent to the hospital, adds the LA Times; three of them are in critical condition.

The quake struck at 3:20 local time, with an epicenter three miles northwest of American Canyon in Napa. It was relatively shallow, with a depth of 6.7 miles; a series of aftershocks have since rattled the area.

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PHOTO: Getty Images