The Station fire, which has destroyed 21 homes and killed two firefighters, was burning within a quarter of a mile of Mt. Wilson as firefighters prepared for another long, hot day.

Inspector Edward Osorio of the Los Angeles County Fire Department estimated property damage from the fire at $7,671,000 and rising.

The fire is expected to move in a northeasterly direction, and officials are putting significant resources on the northern edge of the fire near Acton.

Officials said the goal for today was to keep the fire west of Highway 39 and Angeles Crest Highway; south of Highway 14, Pearblossom Highway and Highway 138; east of Interstate 5 and north of the foothill communities along the Angeles National Forest border. Mt. Wilson was believed doomed last night, but Osorio said aggressive brush clearance by crews and drops of fire retardant from the air seem to have helped.

"At this point, I don't think it suffered any serious damage. We'll probably get some flare-ups or threatening flame activity, but we don't think it's going to be a major problem," he said.

The Station fire doubled in size to 85,000 acres overnight and destroyed more structures.

"That fire burned just like it was daytime. Usually you get recovery because humidity goes up at night, which slows the fire down and you're able to construct more line around the fire," said U.S. Forest Service spokesman Nathan Judy. "But last night that wasn't the case." The exact number of homes consumed by the Station fire remains unclear, but officials said several homes south of Acton were lost last night and this morning. Earlier, 18 homes in the Tujunga Canyon area were lost, but officials expect that number to rise.

More neighborhoods were evacuated overnight as the fire pushed in three directions.

"We are making progress, but it is very slow and very dangerous," incident commander Mike Dietrich of the U.S. Forest Service said at a news conference this morning. "We have to wait for the fire to come to us."

At the bottom of Mt. Wilson Road early this morning, firefighters bedded down in the ash-flecked open air, the forest pitch black except for the flames lighting ridgelines in the near distance. The head of the fire appeared to be across a broad and deep canyon from the Mt. Wilson compound.

Smaller flare-ups could be seen closer to the thicket of communications towers alongside the Mt. Wilson observatory, where five engine crews were posted overnight.

The blaze already had raced up to the winding stretch of Angeles Crest Highway that leads to Mt. Wilson Road. Road signs had melted, guardrails were burned free of their wood moorings, and the switchbacks were choked with fire-loosened boulders and scorched tree limbs.

Two firefighters were killed when they drove off the side of a treacherous road in the Mt. Gleason area, south of Acton, around 2:30 p.m. Sunday, said Los Angeles County Deputy Fire Chief Mike Bryant. They were later identified as Arnaldo Quinones, 35, of Palmdale and Tedmund Hall, 47, of San Bernardino County.

"This accident is tragic," Bryant said, choking up as he spoke Sunday evening. "This is a very difficult time for L.A. County Fire Department and the men and women that serve day in, day out."

The fallen firefighters were overseeing workers clearing brush at a Department of Corrections inmate campsite, Osorio said.

"It's still under investigation, but apparently the campsite got overrun by fire," he added.

More than 12,500 homes were threatened, and 6,600 were under mandatory evacuation orders Sunday night. Twenty-one residences have been destroyed, fire officials said, mostly in the Big Tujunga Canyon area.

The fire was 5% contained, officials said, and at least temporarily had eased off in foothill communities from La Cañada Flintridge to Altadena.

Much of Sunday turned into a blistering-hot waiting game for firefighters, who were trying to determine where the fire would move next. Rather than battling the flames in the sheer granite canyons of the interior, with heavy vegetation more than 40 years old in many areas, they cut fire lines near threatened neighborhoods.

"In this rugged, steep terrain, with this brush as thick as it is, we are having difficulties establishing containment lines where we can make a stand," said Capt. Mark Savage, a spokesman for the Los Angeles County Fire Department. "This fire is still very much out of control."

Fire was burning all around Angeles Crest Highway near Mt. Wilson on Sunday evening. Earlier, hand crews cleared brush to protect the historic observatory and critical transmission towers for local television and radio stations.

The century-old observatory holds what was for decades the largest telescope in the world; it was instrumental in many of astronomy's biggest discoveries, including research that led to the "big bang" theory.

"It's a serious situation. Is the observatory going to make it? We're doing everything in our power. But I wouldn't be surprised if it is impacted by fire today or tomorrow," Bob Shindelar, operations branch director of California Incident Management Team 5, said Sunday afternoon.

More than 2,800 fire personnel from around the state have converged to battle the Station fire, along with 12 helicopters and eight air tankers.

They had hoped that the day would bring cooler, more humid air. But the red-flag fire alert was extended through today as the fire grew in all directions and sent a column of smoke high into the air -- mushrooming into a towering pyrocumulus cloud that could be seen across the Southland.

Meteorologists predicted that hot, dry conditions would continue without relent until at least Tuesday.