Update, 8:30 a.m., Sunday: Cal Fire says the blaze remains at 4,300 acres burned and is now 80 percent contained. All road closures have been lifted and a total of four injuries have been reported.

Update, 8:45 a.m. Friday: Cal Fire reports as of 8 a.m. that the Butts Fire is 55 percent contained and the acreage burned remains at 4,300. All evacuation orders have now been lifted. The Napa Valley Register last night reported that some residents who had been evacuated have already returned home. Two residences and seven outbuildings have been destroyed.

If you're interested in firefighting details, Cal Fire's got them:

Total Fire Personnel:	1,725
Total Fire Engines:	128
Total Fire crews:	60
Total Airtankers:	4
Total Helicopters:	11
Total Dozers:	12
Total Water Tenders:	13

Update, 3:15 p.m. Thursday: Officials have lifted an evacuation order for part of the fire zone, allowing residents of Lake Berryessa Estates and areas at the northern end of Pope Valley to return home. Cal Fire is now putting the number of residences threatened by the blaze at 180, down from 380 earlier today.

The latest report on the size and status of the fire: 4,300 acres, with 30 percent containment — the same as early this morning. About 1,100 firefighters are fighting the blaze.

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One of our Facebook readers has asked what it means that the containment percentage has stayed the same since Wednesday morning as the acreage has continued to grow. Does it means firefighters are at a standstill?

The containment number that Cal Fire uses refers to the rough percentage of a blaze's circumference that's bordered with completed firelines (also commonly called control lines or containment lines). An excellent glossary of wildland firefighting terms from public radio station KPCC in Los Angeles defines a fireline this way:

The manmade portion of a control line, this is a strip of land that has been dug or scraped down to the layers of soil below the surface that have little combustible material and are unlikely to burn. Fireline is built by hand crews to help complete a control line and contain a fire. The larger the flames and the worse the conditions, the wider the fireline will have to be to contain the oncoming wildfire.

So, let's say you have a fire with a circumference of 6 miles. If you had achieved 30 percent containment of that fire, you could infer you had 1.8 miles (30 percent of 6 miles) of firelines in place. The fire might still expand along the rest of the circumference, 4.2 miles.

Now, let's fast-forward a couple of days, and your fire has grown. It has a circumference of 12 miles. You still have 30 percent containment. With 30 percent containment, your firelines have now grown to 3.6 miles, while the uncontained perimeter has grown to 8.4 miles. If things keep on that way, well, you'll have a big problem on your hands.

That's why Cal Fire and other agencies tend to try to throw a lot of resources at rapidly growing fires that occur anywhere close to populated areas — get them contained before they become big problems. The reason fire containment has stayed at 30 percent on the Butts Fire is due to the abundance of extremely dry vegetation, the steep landscape where the blaze is burning, and the hot, occasionally windy weather.

Cal Fire says crews have also been detailed to defend the threatened residences in the area, a job that diverts resources away from the job of building containment lines.

Update, 8:20 a.m. Thursday: Cal Fire says the Butts Canyon blaze has burned 4,300 acres as of early this morning and is still 30 percent contained as a massive firefighting force continues to try to get ahead of it.

The agency has also updated its damage, now saying the fire has destroyed two residences and seven outbuildings since it broke out just after noon Tuesday. About 380 homes are still threatened and evacuation orders for the nearest rural communities in northeastern Napa County and southern Lake County remain in place. The site of the fire is 30 miles northeast of the city of Napa and a few miles to the northwest of Lake Berryessa.

Dozens of those forced from their homes have been staying at a Red Cross emergency shelter at the high school in Middletown, with officials reportedly telling them they may not be allowed to go back home.

KQED's Ted Goldberg talked Thursday morning to Beth Hall, a waitress at the Cowpoke Cafe, just down the street from the evacuation center. She said her new customers over the last few days want more than just food.

"They're asking me questions 'cause they don't what's going on," Hall said. "If I've heard anything about the fire, if there's any news, do they know when they get to go home."

Cal Fire says 1,067 firefighters are working the blaze, along with four fixed-wing air tankers and half a dozen helicopters.

Update, 4:45 p.m. Wednesday: Cal Fire has just released an update on the status of the Butts Fire, burning on the border of Napa and Lake counties about 30 miles northeast of the town of Napa.

The agency says the fire has now consumed 3,800 acres of grassland and mixed woodland, and is still 30 percent contained. (That's about 6 square miles, and in San Francisco terms would be equivalent to the area enclosed in a box bounded by lines running from Fisherman's Wharf to AT&T Park, from AT&T over to Mission Dolores Park, from the park up to the Palace of Fine Arts, then back to the wharf.)

Evacuation orders for the rural area, near the northern tip of the Pope Valley, remain in place. About 380 structures are reportedly threatened. Residents who have left their homes have been told it could be three days before they're allowed to return. About 700 firefighters are in action against the blaze, with support from four air tankers and seven helicopters.

Update, 8:45 a.m. Wednesday: Cal Fire says the Butts Fire, burning in northeastern Napa County, grew to 3,200 acres overnight. Firefighters have it 30 percent contained. It has destroyed five buildings and is threatening hundreds more, forcing some homeowners in the area to evacuate.

"Overnight the temperatures and the weather aided us in the firefight. It slowed this fire down," said Cal Fire spokesman Daniel Berlant. "Yesterday it was burning at an explosive rate."

No injuries have been reported.

Update, 6 p.m. Tuesday: The Butts Fire in rural Napa County is spreading quickly, burning 2,500 acres. However, firefighters have contained 30 percent of the blaze. Cal Fire spokesman Daniel Berlant attributed the quick movement to the area's dry conditions.

"The year's drought has left much of the grass and brush six to eight weeks drier than normal, so right now we're experiencing conditions that we would typically see toward the end of August, and that's why a fire like this is able to burn so rapidly," Berlant said.

Please visit Cal Fire to track firefighters' progress.

Update, 5:30 p.m.: Cal Fire spokesman Daniel Berlant reports that the Butts Fire has spread to 1,000 acres and is still threatening homes just northwest of Lake Berryessa in Napa County. Firefighters from the state and three counties have continued to contain 10 percent of the fire. That means they're actually gaining on the rapidly growing blaze, Berlant said.

"With how rural this fire is, with the access being challenging and with the weather conditions, this fire has continued to grow," Berlant said. "We'll continue using our aircraft, the helicopters, the air tankers making water drops, retardant drops, slowing down this fire, so those ground resources can continue to build the containment line and put the fire out," Berlant said.

Update, 5 p.m.: The fire burning in Napa County has spread to 600 acres and damaged five structures, according to Cal Fire. State firefighters and crews from Napa, Lake and Solano counties have contained about 10 percent of the blaze.

Update, 3:50 p.m.: Cal Fire is reporting the fire burning in northeastern Napa County is about 10 percent contained and that mandatory evacuation orders have been extended to cover about 180 homes. Smoke from the fire, burning about 30 miles northeast of the city of Napa, is visible throughout the North Bay.

Some details by way of the Napa Valley Register:

The fire has already scorched at least 500 acres in the Pope Valley area, according to Cal Fire.

The blaze reportedly was threatening several buildings in Pope Valley, according to the Napa County Sheriff's Office.

There are mandatory evacuations for the west side of the 7800 block of Butts Canyon Road north of Snell Valley Road, according to the Sheriff's Office. Berryessa Estates has also been evacuated, and Aetna Springs Road is closed.

As of 3 p.m., sheriff's deputies were using bullhorns to order the evacuation of residents at Berryessa Estates.

John Hallman, a longtime resident at Lake Berryessa Estates, was going to houses of medically disabled and elderly residents to help them evacuate the area. The residents will head to Middletown, he said. Because of the fire, the residents cannot reach Pope Valley School, where Napa County Red Cross is setting up a shelter.

"We’ll have a place for people to gather to determine the next step,” said Anne Steinhauer, executive director of Napa County Red Cross.

Original post: Cal Fire has rushed crews to the scene of a rapidly growing wildfire in a remote part of northeastern Napa County.

The blaze broke out about noon Tuesday on the northern end of Pope Valley along Butts Canyon Road. The fire quickly burned across 500 acres and destroyed several structures, though no homes. The scene of the fire is about 10 miles northeast of the town of Calistoga and across a mountain ridge from the Napa Valley.

Cal Fire spokesman Daniel Berlant said Napa County sheriff's deputies had evacuated about a dozen homes in the area, which is a mix of ranches, vineyards and open chaparral. According to Berlant:

This is a very rural area. There's not a lot of homes and those homes that are there are on several acres, so there's a lot of open land, a lot of undeveloped land. So as this fire continues to grow, it's doing a lot of destruction to the trees and the grassland, but fortunately there's not a lot of homes in the immediate area.

There was no immediate word on how the fire started.

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Berlant said weather in the area is not extreme, with a temperature of about 90 and a 10-12 mph wind gusting to about 15 mph. The National Weather Service has declared a red flag warning through Tuesday evening for areas of the Coast Range further north, as well as throughout the Sierra Nevada from Yosemite National Park north. Thunderstorms and dry lightning are possible throughout the warning area.

Pope ValleyPope Valley

Butts Blaze North of Napa 80 Percent Contained