Update, 8:20 a.m. Tuesday: Scores of small aftershocks have followed the Sunday morning temblor, including an attention-getting cluster of quakes early Tuesday. The U.S. Geological Survey reports the strongest of those was a 3.9-magnitude shake at 5:33 a.m. centered just south of Napa. That was followed by shocks of 2.7, 1.9, 2.8 and 3.0 over the next 72 minutes. We haven't heard any reports of damage following the series of small quakes.

In Vallejo, demolition crews took down a portion of an unstable bell tower at the First Baptist Church. The tower was deemed dangerous after an inspection Monday and surrounding streets, including Sonoma Boulevard (Highway 29) were closed until the hazard was removed.

Update, 5:15 p.m. Monday: Continuing fallout from Sunday's South Napa Earthquake: Officials in Vallejo have closed a two-block stretch of one of the city's principal streets because of concerns that a church bell tower could collapse, and Napa's school district announced that schools will remain closed Tuesday and possibly beyond.

KQED's Craig Miller reports that Vallejo's First Baptist Church, at the corner of Carolina Street and Sonoma Boulevard, has been red-tagged. Among the church's structural concerns: that the bell tower has been weakened to the point where it might collapse. This fear has prompted officials to close Sonoma Boulevard, which is also Highway 29, for two blocks on either side of the church. The closure also affects Lincoln Elementary School, immediately across the street from First Baptist.

Dave Kleinschmidt, Vallejo's public works director, said the city hoped to partially demolish the tower late Monday or Tuesday morning and that Sonoma Boulevard will remain closed until that job is done. First Baptist is one of 10 buildings in the city that have been red-tagged, or declared unsafe for occupation, at least for the time being. Another 34 buildings have been yellow-tagged, deemed safe to enter but not to stay in.

Napa officials updated the number of buildings red-tagged there to 64. Among the buildings shut down is the city's historic courthouse building, and county officials announced today that the building will be closed indefinitely as it undergoes structural analysis.

Several other major public buildings, including the Napa County Administration Building, were closed Monday.

The Napa Valley Unified School District announced schools across the city will remain closed Tuesday as staff cleans up after the quake. The district will make a decision Tuesday about whether the closure will be extended.

Update, 10:55 a.m. Monday: KQED reporter Mina Kim says that hardhats and orange vests are the order of the day in downtown Napa as the city begins the process of recovering from Sunday morning's 6.0 earthquake.

"There's a lot of activity downtown," Kim says. "All the street closures in the area are still in effect. Damaged buildings still have police tape around them. There are more bricks in the street today because crews are taking down damaged facades and they're starting to clear them."

David Gadlin, manager of the Lucero Olive Oil store in downtown Napa, started work at 5:30 a.m. Monday to finish cleaning up so the business could open on schedule at 10 a.m.

The Lucero store was widely pictured as one of the businesses damaged in the quake, with olive oil and balsamic vinegar flowing and seeping under the store's front entrance. Today there's a pile of kitty litter near the front door, used to soak up Sunday's oozing mess.

"It took a lot of paper towels, rags and cat litter to pick up the oil," Gadlin says. "And now we're making sure we get rid of all the cat litter and all the stickiness, and I'm sure we'll be finding it in strange places for weeks to come."

Gadlin says about 500 bottles of olive oil and balsamic vinegar were smashed when thrown from shelves during the quake. He estimates the retail value of the lost inventory at about $10,000.

"It could be a lot worse," he says. "Nobody got hurt. It happened in the middle of the night, and we got lucky."

Among the bigger postquake disruptions in Napa today:

The Napa Valley Unified School District, with schools in Napa and Yountville, has shut down for the day so staff can clean up classrooms. The county administration building, its interior a shambles after the quake, is also closed.

Officials in Vallejo are also assessing buildings along a Tennessee Street commercial strip and on Mare Island, where several historic buildings were closed for postquake inspections. Officials estimated Monday that structures in the city sustained about $5 million in damage.

9:35 p.m. Sunday: Napa officials are advising residents who lost water service completely for any period of time after today’s earthquake to use bottled water, boil their water before drinking or get water from the station set up by the city on Pearl Street one block west of Main or at the Las Flores Center on Linda Vista Avenue. Officials say water is safe for bathing and other household uses.

5:30 p.m.: 7,600 residents in Napa County are still without power, while full power has been restored to Sonoma County. Napa City Manager Mike Parness said that PG&E informed him that full power would be restored to Napa residents 1 p.m. Monday at the latest.

According to Napa Community Development Director Rick Tooker, 33 buildings have been red-tagged, or deemed unsafe, while an unknown number of buildings have been yellow-tagged ("owners should be going in only to clean the premises.") The 33 buildings deemed unsafe are a combination of older unreinforced masonry and newer constructions, some of which have had recent retrofit work done, according to Tooker.

Napa Public Works Director Jacques Larochelle said that 60 properties in the city are currently without water, but that all repairs to restore water to the properties (a mix of commercial and residential) are expected to be completed by Wednesday or Thursday of this week.

4:50 p.m.: Walt Mickens, CEO of Napa's Queen of the Valley Hospital, just reported that the facility has treated 172 people since the quake struck at 3:20 a.m. and that patients continue to arrive with quake-related injuries.

Of those 172 people, 159 were treated and released with injuries such as lacerations and bruises; 13 patients were admitted, including seven with what he called "orthopedic conditions" -- broken bones -- five with respiratory or cardiac conditions, and one person whose condition was not related to the quake.

3:55 p.m: According to California Governor's Office of Emergency Services Director Mark Ghilarducci, 90-100 homes in total have been red-tagged at this point.

Briefing the media after assessing damage to the region, Ghilarducci said O.E.S. has received reports that shaking was felt as far north as Ukiah and as far south as Salinas. "While the damage was bad, it's not as bad as it could've been."

According to California State Geologist John Parrish, there have been roughly 50 to 60 aftershocks since Sunday morning's quake, the strongest being 3.6. While geologists don't expect another large earthquake, aftershocks are expected to continue with decreasing magnitude and importance for several weeks.

"This is a reminder that we live in earthquake country. None of us are immune to this," Parrish said, while urging residents in and around Napa to replenish earthquake supply kits and be cautious about what structures you enter.

Parrish also explained that the geology around the epicenter, consisting predominantly of soft muds, helped reduce the scope and scale of the damage by reducing shaking at ground level.

2:45 p.m.: Residents of Vallejo were also hit hard by this morning's earthquake. Congressman Mike Thompson told KQED that 41 buildings had been red-tagged, deemed unfit for habitation. There have also been 16 water main breaks. The Mare Island Maritime Museum and old officers' mansions have all sustained damage and lost their chimneys. The U.S. Forest Service building also had a major water main break.

"They've had a considerable damage. Especially down in the Tenneessee Street area and over on Mare Island," said Thompson.

1:53 p.m.: About 16 buildings in Napa City have been red-tagged, said city officials. Historic buildings have also sustained damage. Four mobile homes were destroyed after a fire at the Napa Valley Mobile Home Park in north Napa. Two other fires in residential areas were extinguished by Napa fire crews.

More than 100 people have called about natural gas leaks, said Napa Fire Chief Mike Randolph. If you smell gas, call PG&E at 1-800-PGE-5000. If you have shut off your gas service, do not turn it back on.

About 17,000 PG&E customers are still without power, most of them in the city of Napa. When the earthquake hit, about 70,000 homes lost power in Napa, Sonoma and Vallejo.

All public schools in the city of Napa and the Justin Siena Catholic High School are closed on Monday. Napa Valley Unified District teachers still need to report. Sonoma State University will be open.

Officials report that several Napa County services will be unavailable on Monday, according to county officials. Damage to the county building at 900 Coombs St. is too extensive to open to the public.

Neither assessor, recorder-county clerk nor Election services will be available to the public tomorrow, according to John Tuteur, county clerk.

"We are working with the Board of Supervisors, Information Technology and Public Works to restore services at an alternate location as quickly as possible," Tuteur said.

12:30 p.m.: About 120 patients have been treated for earthquake-related injuries, said Queen of the Valley President Walt Mickens. Fewer than 10 were admitted, and three are still in critical condition.

“The majority of injuries are non-life threatening: lacerations, cuts, abrasions, bumps and bruises. One patient has multiple fractures. One heart attack. A handful are being admitted to the hospital. Most are treated and released,” Mickens said.

However, Mickens warned residents to be careful, saying that many of the new injuries stem from cleanup efforts.

About 60 water lines are currently down, said Director of Public Works Jacques LaRochelle at a city press conference.

How big was the earthquake? Although the shaking lasted a long time, its intensity was much lower than the Loma Prieta Earthquake.

10:25 a.m.: A one-line message from the California Highway Patrol gives the all-clear for motorists headed to major sporting events today: "CHP - GOLDEN GATE: EARTHQUAKE UPDATE: All bridges/roads in CHP jurisdiction safe for travel. Access to Sonoma Raceway/Levi Stadium open."

Here's a link to the CHP's detailed summary of post-quake road conditions in the region: Earthquake Update (via Nixle)

Thanks to KQED's Sarah Baughn for the heads-up on that.

10:15 a.m.: A clarification on the earthquake magnitude: The U.S. Geological Survey is, as of this very moment, calling the South Napa Earthquake a 6.0-magnitude event. A couple hours ago, the USGS had moved the magnitude up to a 6.1 shake. Before that, it was rated at 6.0. And immediately after it happened, it was rated a 5.9. This obviously makes it hard to choose a number to put in a blog post, but we're going to go with what's current from the USGS. So back to 6.0 we go until the agency recalculates again. (We understand from listening to USGS scientist David Oppenheimer earlier this morning that there were some "rounding" issues in rating this quake.) And: We apologize for any discrepancies in the numbers we've displayed to this point.

9:45 a.m.: The transit impact of the South Napa earthquake, as reported by Bay City News:

Amtrak's Capitol Corridor train service has been temporarily suspended this morning between Sacramento and San Jose while crews inspect the tracks for damage following the earthquake early this morning near American Canyon.

ACE special train service between Stockton and San Jose for this afternoon's San Francisco 49ers football game at Levi's Stadium in Santa Clara has also been canceled because of safety concerns following the quake.

Caltrain officials said they expect to run service to the football game but said there are delays this morning because of track and bridge inspections.

BART had pre-planned delays because of track maintenance on its Pittsburg-Bay Point line but has not reported any other disruptions this morning as a result of the quake.

Update, 9:20 a.m.: Napa city officials are briefing the media on the impact of the earthquake in the city.

Jack LaRochelle, Napa's public works director, said the most urgent issue is damage to the city's water system. He said there are about 30 significant water main breaks, most in the Browns Valley area on the city's west side. He said the city's water plants are fine and are tapping a second source of water, from Lake Hennessey, northeast of the city.

He had no immediate estimate of the number of buildings that have been or will be red-tagged because of earthquake damage.

City officials said they have gotten about 100 reports of gas leaks from residents and that PG&E crews have been responding.

Update, 9:10 a.m.: To summarize:

A 6.0-magnitude earthquake epicentered at the southern edge of Napa struck at 3:20 a.m. The quake is the strongest to strike the Bay Area since the Loma Prieta quake of Oct. 17, 1989.
The U.S. Geological Survey link to seismic details on the quake: Napa-North Bay Earthquake
So far, 87 injuries have been reported in Napa. Three people were critically injured.
Widespread damage is reported in the city of Napa ranging from burst water mains to the collapse of commercial building facades in downtown Napa to extensive exterior and interior damage of single-story homes in the surrounding area.
Several major fires started after the quake, including one in a mobile home park.
PG&E reports tens of thousands of homes have been without power in Napa and Sonoma counties and Vallejo in Solano County.
The California Highway Patrol and Caltrans are assessing damage to roads in the North Bay. Numerous pictures of buckled roads have appeared on Twitter. A major interchange at the Vallejo end of Highway 37 has been closed because of roadway damage, though Highway 37 remains open.
Geologists say the chance of a magnitude 5 aftershock in the next seven days is 54 percent. The chances of a quake larger than the main shock in the next week is 5 to 10 percent. More than a dozen aftershocks followed the Sunday quake, the strongest a 3.6 shake at 5:47 a.m.

Update 8:30 a.m.: Here's a quick list of quake impacts from the city of Napa:

INJURIES: 87 patients have been treated or are being treated at Queen of the Valley Hospital. There are three critically injured persons, 2 adults and one child.
Four mobile homes destroyed and two others damaged by fire on Orchard Avenue in north Napa.
GAS LINES: Crews are responding to reported gas line breaks in a variety of locations.
WATER MAINS: There are approximately 30 water main leaks. Both water treatment plants running, no damage. Some areas have no water due to main breaks and some areas no or low pressure. Water remains safe to drink.
City crews are assessing infrastructure damage and damage to homes and other buildings.
Historic Buildings damaged:
• Sam Kee Laundry
• Goodman Library
• Napa County Courthouse
At least two commercial buildings in the downtown area are also severely damaged.
SHELTERS: The Red Cross evacuation center has been set up in the Napa High School gym.
Drop boxes for debris will be placed at all public schools.

Update: 8:15 a.m.: From the Associated Press accounts of the quake:

California Gov. Jerry Brown said in a statement this morning the impact of the earthquake is being felt throughout the region.

"My Office of Emergency Services has been on full activation since early this morning and is working close with state and local emergency managers, first responders and transportation officials to respond to impacts to residents and critical infrastructure," he said. "These safety officials are doing all they can to help residents and those living in affected areas should follow their guidance and instruction."

And again from AP, a Napa emergency responder:

"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, who said he had to climb over fallen furniture in his own home to check on his family before reporting to duty, said he was starting to see more reports of injuries.

The shaking emptied cabinets in homes and store shelves, set off car alarms and had residents of neighboring Sonoma County running out of their houses and talking about damage inside their homes. Officials say widespread power outages have been reported in the area.

Update, 7:50 a.m.: Again, by way of KCBS: Queen of the Valley Hospital is reporting having treated 87 people injured in this morning's earthquake. Three of those injuries are reportedly critical -- a child hit by falling masonry and two adults with undescribed injuries. The rest of the injuries have been minor, including lacerations caused by flying glass.

Update, 6:10 a.m.: By way of an interview on KCBS: David Oppenheimer of U.S. Geological Survey is saying that this morning's earthquake occurred on the West Napa Fault, and the agency has named the event the South Napa Earthquake.

Meantime, reports of damage continue to come in from downtown Napa. In the area that suffered the most severe damage, building facades have collapsed and chunks of buildings continue to fall in the streets.

The San Francisco Chronicle reports: "Napa Fire Capt. Steve Becker said there were "numerous" injuries reported across Napa, but details were not immediately available."

Update, 6 a.m.: An account by way of the Santa Rosa Press-Democrat of one major fire in Napa:

A fire ripped through more than 10 units at Napa Valley Mobile Home Park, off Orchard Avenue. Four homes in the complex were a total loss, with up to eight additional units suffering minor to moderate damage, Napa Fire Capt. Steve Becker. No injuries were reported, but dozens of residents were evacuated to the complex’s clubhouse.

The damage at the mobile home park appeared to be the worst in the Napa area, Becker said. The cause was under investigation, but appeared to be linked to gas line ruptures, he said.

Resident Andre Van Derheyden said he and his wife were jolted awake by the quake.

“It blew us out of bed,” he said.

By the time the couple were able to gather their dog and get outside, the mobile home next door was on fire, he said. The resident, a woman, was able to escape, but her home was a total loss.

“Thank heaven we are fine, but I feel so bad for my neighbor,” said Van Derheyden.

Update, 5:50 a.m.: To summarize:

A 6.0-magnitude earthquake epicentered at the southern edge of Napa struck at 3:20 a.m. The 6.0 quake is the strongest to strike the Bay Area since the Loma Prieta quake of Oct. 17, 1989.
The U.S. Geological Survey link to seismic details on the quake: Napa-North Bay Earthquake
Injuries have been reported in Napa, but there are no authoritative reports yet as to the number or severity.
Damage is reported in the city of Napa ranging from the collapse of commercial building facades in downtown Napa to extensive exterior and interior damage of single-story homes in the surrounding area.
Witnesses are reporting two major fires at the northern end of Napa, one possibly in a mobile home park.
PG&E reports thousands of homes are without power in Napa and Sonoma counties and Vallejo in Solano County.
The California Highway Patrol and Caltrans are assessing damage to roads in the North Bay. Numerous pictures of buckled roads have appeared on Twitter. A major interchange at the Vallejo end of Highway 37 has been closed because of roadway damage, though Highway 37 remains open.
Geologists say the chance of a magnitude 5 aftershock in the next seven days is 54 percent. The chances of a quake larger than the main shock in the next week is 5 to 10 percent. Two small aftershocks have been recorded so far: a 2.5-magnitude shake at 5:01 a.m. and a 3.6 shake at 5:47 a.m.

Update 5:05 a.m.: KQED's Craig Miller checks in from the Mare Island Bridge on Highway 37:

I talked to a guy from Caltrans who says he is the bridge supervisor. He said he wasn't aware of any bridge closure, though he said there was damage to Sonoma Boulevard [nearby in the city of Vallejo] where pavement had buckled. There are emergency vehicles on the bridge, but I can also see traffic moving across it.

KCBS is carrying a witness account from Rob Downey, a Napa business owner, who reports severe damage to several historic buildings in downtown. He said damage seemed to be concentrated near in a quadrant bounded by Main, Second, Third and Brown streets.

Update 4:55 a.m. More details from KQED's Craig Miller in Vallejo: He's been at the scene of a single commercial block of Tennessee Street near intersection of Broadway where there's significant damage:

There are at least seven storefronts, including a Chase Bank, with windows blown out. In some cases, glass had blown out into the middle of the street. This was a block with about seven different businesses, including a music story, a bridal store and a jewelry store. You can see that part of the ceiling or roof is coming down in the music store. It's really kind of bizarre -- here's one block in Vallejo with all this damage, and then when you look across the street everything is fine.

Craig's on his way to check on the situation at the Mare Island Bridge in Highway 37, which has been reported closed because of possible quake damage.

Update 4:35 a.m.: From all the reports we've heard over the last hour-plus, it's apparent that the worst of the damage from this morning's quake is focused in the city of Napa and surrounding communities.

Unconfirmed reports -- unconfirmed -- relayed by KCBS say there's been some road and possible bridge damage on Highway 12 in Napa and Highway 37 in Vallejo.

KCBS reporter Curtis Kim went on the air with a report that the California Highway Patrol was closing one of the Highway 37 bridges in Vallejo. We're not sure from the report which bridge it is.

Update, 4:25 a.m.: KQED's Craig Miller is touring the streets of Vallejo and says there are signs of emergency response in the areas he's seen -- damage to some building and sirens.

From KQED's Scott Shafer: Cheri Hansen of the Napa County Sheriff’s office says: “Everything’s upside down here. Things have flown out of the cabinets. My computer flew off the desk. We have power because we have a generator.”

Update, 4:08 a.m.: KQED reporter Mina Kim lives in Napa, near the epicenter of this morning's earthquake. She said she experienced violent shaking. In her words, "Everything came down" from the walls. "Our refrigerator moved across the kitchen. All the shelves came down." She said she and her husband turned off their gas and are assessing the damage. She also reported a fire is visible in the distance, though she's not sure what's burning.

Todd Smoot, a KCBS editor, came on the air to report a major power outage in large parts of the Sonoma Valley.

By way of KQED's Scott Shafer, who just got off the phone with the U.S. Geological Survey, here are a few more details on where and when the quake struck from Frank Baldwin, a USGS geophysicist in Golden, Colorado:

"It was felt over a wide area. It's a shallow quake and we haven't heard any reports of damage, although it has the potential for damage.

It's about 6 miles deep and usually when you have a shallow quake it generates more surface waves, which are felt more predominantly throughout the region.

The fault line has not been determined yet, but we'll be looking at that over the next hours or days by the Northern California seismic network."

Updated 3:45 a.m.: The U.S. Geological Survey has recorded an earthquake that rolled through the Bay Area at 3:20 a.m. and 44 seconds.

USGS data shows the quake was a 6.0 quake that struck between Napa and the community of American Canyon. That's the approximate location of the Rogers Creek Fault in the North Bay. The USGS reported the depth of the epicenter as 10.8 kilometers, relatively shallow.

This was an unusually long earthquake compared with most recent shakes in the Bay Area, lasting at least 10 seconds, with many callers to KCBS in the immediate aftermath saying they felt movement for as long as 20 seconds. In Berkeley, where this account is being written, the quake was a continuous side-to-side shaking as opposed to a strong, abrupt shock.

The U.S.G.S. "Did You Feel It" page showed the quake was felt across the Bay Area from Sonoma through Santa Cruz County. So far, we have no reports of damage.

West Napa FaultWest Napa Fault

South Napa Earthquake: City Says There's Over $300 Million in Damages

South Napa Quake: What Scientists Know So Far