UPDATE 7:00 p.m.
Firefighters hope to take advantage of cooler temperatures, higher humidity and dying winds tonight to battle the brush fire still burning in a remote area in the San Gabriel mountains.
“There’s nothing up there. It’s what we call a rattlesnake ridge," said U.S. Forest spokesman Nathan Judy. "The fire was working in that area and that’s what you saw this afternoon, is the smoke going up. It was just the fire was burning around that one portion of the fire. “
Judy said crews are calling on more air tankers to drop fire retardant and create a containment line on the west side of the fire.
UPDATE 4:00 p.m.
Tony Imbrenda of the L.A. County Fire Dept. has said the brush fire is now "considerably larger" than 4,000 acres. The department is currently doing reconnaissance to figure out how munch larger.
"I would not say it is improving right now," he said. "I wouldn’t characterize it as dramatically deteriorating, but we do have a significant rate of spread right now.”
Fire crews' goal is direct the fire to an area they can contain it, said Imbrenda, but steep terrain is making that difficult.
Most of the attack is coming from the air – helicopters and planes dropping water and fire retardant.
Around 1,100 people were evacuated Sunday night, mostly campers and about a hundred seasonal home vacationers.
KPCC's Erika Aguilar is at the scene. Follow her on Twitter for updates:
Red Cross LA says they'll be moving 2 families (2 adults, 3 children) frm Glendora HS, evacuation center to temporary motels.— Erika Aguilar (@erikaaaguilar) September 3, 2012
UPDATE 12:54 p.m. U.S. Forest Service public information officer Nathan Judy explained the threats facing firefighters Monday.
"Our biggest concern today will be the winds this afternoon and the steep terrain that our folks have to work in. You have steep terrain anywhere from 40- to 80-degree angle, so it's really steep, really nasty terrain out there, and to get our fire folks out there to cut a line around this fire is the concern — making sure they're out there safely," Judy said.
Some forests allow fires to burn in a controlled fashion, but not in the Angeles, Judy said.
"The Angeles National Forest, we have a no-burn policy. We put all fires out. We don't allow fires to burn on the Angeles, because we're so close to urban areas, if you let that fire burn, you're putting homes and structures at threat, and people's lives," Judy said.
On the first day of the fire Sunday, two firefighters were injured. One from the Los Angeles County Fire Department suffered heat exhaustion, while another injured an ankle.
Firefighters were using six large water air tankers and eight helicopters, Judy said — four medium and four light choppers.
UPDATE 9:23 a.m. Los Angeles Fire Inspector Tony Imbrenda described the challenge of trying to control the 4,000-acre Williams Fire burning north of Azusa in the San Gabriel Canyon area.
"The fire behavior is expected to be intense because of the fact that we are in very steep terrain," said Imbrenda.
He added that wind gusts around 20 miles per hour were expected in the afternoon. Firefighters are also facing low humidity, so they may face a "pretty significant fire intensity" in the afternoon, Imbrenda said.
Estimates Monday were that the fire would take a week to get completely contained.
Thomas Chacon is the U.S. Forest Service is the manager in charge of creating a small city of firefighters and support services for them as they try to bring the Williams Fire under control.
Chacon said up to around 400 fire personnel could be staying there. They might camp there a week or more on the grounds of the Santa Fe Dam Recreation Area.
It's an expensive proposition to set up a camp like this, Chacon said. Firefighters will be able to eat, sleep and shower at the camp.
"They’ll be resting or they’ll be getting their act together here, see what they’re going to be doing for the evening shift," Chacon said.
Hundreds of people celebrating Labor Day are already in the park, having arrived near dawn to claim the best picnic sites.
Highway 39 will be closed Monday and local campgrounds were evacuated.
UPDATE 7:23 a.m. As of early Monday morning, the fire had grown to 4,000 acres with 400 firefighters battling the flames, according to U.S. Forest Service. The fire remained only 5 percent contained as it pushed toward the Sheep Mountain Wilderness area.
Due to the fire burning into a wilderness area, though, no structures looked to be threatened, according to the Forest Service. Firefighters planned to work throughout the day to complete a containment line around the fire in the steep terrain. The winds Monday morning were light, leaving firefighters with one less thing to worry about.
UPDATE 9 p.m. A wildfire broke out in the San Gabriel Mountains above Glendora Sunday afternoon, and by just before 9 p.m. it had grown to 3,600 acres, according to the U.S. Forest Service. There are now 300 firefighters, aided by nine air tankers and four helicopters, attacking the flames. The fire is 5 percent contained, the Forest Service says.
Angeles National Forest spokesman Nathan Judy said the fire was reported about 2:30 p.m. Sunday near State Route 39 above the city of Glendora. The fire's cause is under investigation, but it possibly began as a car fire, L.A. County sheriff's Sgt. Kirk Smith said, according to the San Gabriel Valley Tribune.
Forest Service officials said around 1,000 Labor Day weekend campers and picnickers were evacuated, along with a mobile home community at Camp Williams, and residents of the River Community rehabilitation center. No structures are currently threatened, according to the Forest Service.
KABC-7 reported one power line down and another one on fire.
The fire is moving uphill in a north-northeast direction in steep, rugged terrain, away from the foothill communities to the south.
The blaze started about halfway between Camp Williams and a shooting range on East Fork Road in the San Gabriel Canyon, 3 1/2 miles east of Highway 39, the Forest Service says.
The large gray cloud of smoke was visible throughout the L.A. basin — including by concertgoers at Sunday's FYF Fest.
In 2009, a wildfire in the Angeles National Forest killed two firefighters, destroyed 89 homes and blackened 250 square miles. The Station Fire was the largest in Los Angeles County history.
This story has been updated.