The magnitude-6.0 quake, which ruptured water mains and gas lines and damaged some of the region's famed wineries, sent residents running out of their homes in the darkness. Three people - two adults and a child - were critically injured.
Dazed residents too fearful of aftershocks to go back to bed wandered through Napa's historic downtown, where the quake had shorn a 10-foot chunk of bricks and concrete from the corner of an old county courthouse. Boulder-sized pieces of rubble littered the lawn and street in front of the building and the hole left behind allowed a view of the offices inside.
College student Eduardo Rivera said the home he shares with six relatives shook so violently that he kept getting knocked back into his bed as he tried to flee.
"When I woke up, my mom was screaming, and the sound from the earthquake was greater than my mom's screams," the 20-year-old Rivera said.
While inspecting the shattered glass at her husband's storefront office in downtown Napa, Chris Malloy described calling for her two children in the dark as the quake rumbled under the family's home, tossing heavy pieces of furniture for several feet.
"It was shaking and I was crawling on my hands and knees in the dark, looking for them," the 45-year-old woman said, wearing flip flops on feet left bloodied from crawling through broken glass.
Gov. Jerry Brown declared a state of emergency for southern Napa County, directing state agencies to respond with equipment and personnel. President Barack Obama was briefed on the earthquake, the White House said, and federal officials were in touch with state and local emergency responders.
Napa Fire Department Operations Chief John Callanan said the city had exhausted its own resources trying to extinguish at least six fires after 60 water mains ruptured, as well as transporting injured residents, searching homes for anyone trapped and responding to reports of 50 gas leaks.
Two of the fires happened at mobile home parks, including one where four homes were destroyed and two others damaged, Callanan said. A ruptured water main there delayed efforts to fight the blaze until pumper trucks could be brought in, he said.
Nola Rawlins, 83, was one of the Napa Valley Mobile Home Park residents left homeless by the fire. Rawlins said she was awakened by an explosion after the quake and managed to escape unharmed, but lost all her belongings.
"There were some explosions and it was burning. Everybody was out in the street," she said. "I couldn't get back in the house because they told everybody to go down to the clubhouse, so I didn't get anything out of the house."
The earthquake sent at least 120 people to Queen of the Valley Medical Center in Napa, where officials set up a triage tent to handle the influx. Most patients had cuts, bumps and bruises suffered either in the quake, when they tried to flee their homes or while cleaning up, hospital CEO Walt Mickens said. Three people were admitted with broken bones and two for heart attacks.
The child in critical condition was struck by flying debris from a collapsed fireplace and had to be airlifted to a specialty hospital for a neurological evaluation, Callanan said.
The temblor struck about six miles south of Napa around 3:20 a.m., according to the United States Geological Survey. It was the largest to shake the Bay Area since the magnitude-6.9 Loma Prieta quake struck in 1989, collapsing part of the Bay Bridge roadway and killing more than 60 people, most when an Oakland freeway fell.
Sunday's quake was felt widely throughout the region. People reported feeling it more than 200 miles south of Napa and as far east as the Nevada border. Amtrak suspended its train service through the Bay Area so tracks could be inspected.
Napa City Manager Mike Parness said at an afternoon news conference that 15 to 16 buildings were no longer inhabitable, and there was only limited access to numerous other structures, mostly ones with broken windows. Officials said they were still assessing buildings in the area.
A Red Cross evacuation center was set up at a high school, and crews were assessing damage to homes, bridges and roadways.
"There's collapses, fires," said Napa Fire Capt. Doug Bridewell, standing in front of large pieces of masonry that broke loose from a turn-of-the-century office building where a fire had just been extinguished. "That's the worst shaking I've ever been in."
Bridewell said he had to climb over fallen furniture in his own home to check on his family before reporting to duty.
The shaking, which lasted for 10 to 20 seconds depending on how close a person was to the epicenter, emptied cabinets in homes and store shelves, set off car alarms and had residents of neighboring Sonoma County running out of their houses.
Pacific Gas and Electric spokesman J.D. Guidi said close to 30,000 lost power right after the quake hit, but that number was down to around 19,000 later in the day, most of them in Napa. He said crews were working to make repairs, but it was unclear when electricity would be restored.
The depth of the earthquake was just under seven miles, and was followed by numerous small aftershocks, the USGS said.
"A quake of that size in a populated area is of course widely felt throughout that region," said Randy Baldwin, a geophysicist with the U.S. Geological Survey in Golden, Colorado.
California Highway Patrol Officer Kevin Bartlett said cracks and damage to pavement closed the westbound Interstate 80 connector to westbound State Route 37 in Vallejo and westbound State Route 37 at the Sonoma off ramp. He said there hadn't been reports of injuries or people stranded in their cars, but there were numerous cases of flat tires from motorists driving over damaged roads.