Henry Rodriguez, the public information officer for the Los Angeles County Fire Department, said the fire was 10% contained but had consumed 25,000 acres.
"This fire is the No. 1 priority in the state," Rodriguez said.
Twenty-five homes have been damaged and four people have been hurt, he said. About 800 people were evacuated Sunday.
"One of the challenges we're having with all the fires is getting [crews] coming in. We're doing the best we can with what we have," Rodriguez said.
FOR THE RECORD:
An earlier version of this article said 800 people had been evacuated. Eight hundred homes were evacuated.
He said the fire grew overnight because of the winds, which were 35 to 40 mph with gusts of up to 65 mph.
There were no new mandatory evacuations in effect, but officials said they were watching the situation. About 3,800 homes are threatened, according to Deputy Fire Chief Glenn Massey.
Karen Cayley, 55, a lifelong California resident, figured a wildfire might threaten her one day. She thought she knew the drill.
There would be some kind of warning, she thought. Even if she had to evacuate her home in Agua Dulce, between Santa Clarita and Palmdale, she would be able to collect a few essentials -- family photos, pets -- before leaving.
She had just started loading up Sunday and had her dog inside the car when a firefighter approached.
"Go now," he ordered her. "Don't take anything. Just go."
And she did -- so quickly that she had to leave everything else behind, including photos and two cats.
Of more than a dozen wind-swept firestorms that erupted across Southern California on Sunday, none, it appeared by nightfall, was more ferocious than the one dubbed the Buckweed fire.
The flames moved so rapidly that firefighters had to move their command center five times to keep ahead of them.
By 7 p.m. Sunday, the blaze had moved 10 miles west into Canyon Country, east of Santa Clarita. Smoke blanketed virtually the entire Santa Clarita Valley, and flames could be seen over numerous nearby ridges.
Paul Smith, 43, walked out of his house in the 19000 block of Newhouse Street in Canyon Country about 5 p.m. Sunday and saw flames on a nearby ridge.
"It started off with a small flame," he said. "Then it just started jumping and started smaller fires. Within five minutes, the whole ridge was on fire, and the flames were 100 feet tall."
Los Angeles County sheriff's deputies ordered mandatory evacuations in Bouquet Canyon, San Francisquito Canyon and North Oaks Park in the Santa Clarita area.
Many residents tried to stay behind to protect their homes, only to be overpowered by wind and flames.
Wayne Pennington, 51, tried to defend his Agua Dulce-area home by using a shovel to pile dirt on flames that were moving toward his home. He had to abandon the effort.
"I'm putting it in the hands of God and the Fire Department," he said.
He was staying with a friend in Palmdale and, like many others, did not know by nightfall if his home had been spared.
By Sunday afternoon in Canyon Country, virtually everyone in the development was leaving, their cars packed with belongings and their headlights on to help them see through the smoke.
A few residents remained, most perched on their roofs to watch the fire.
John Metcalf, 61, has lived in the area more than 10 years.
Metcalf was packing his minivan with blankets, pictures, medication and computer hard drives.
He has two rabbits -- C.C. and Patches -- and he wanted to be sure they weren't left behind. He wasn't sure if he was going to leave, though he had called friends to arrange a place to stay if he decided to.
"We want to be ready in case it happens," he said. "This is the first time we've ever got this close."
Brad Davidson, 38, works at a print shop in West Los Angeles. At his home in the 27000 block of Crosspath Street, just off Whites Canyon Road in Canyon Country, he was packing his family's belongings into two cars.
The fire was about half a mile north when he got a call from his boss. "I think you'd better have someone else in tomorrow," he told his boss. "You can't see. You can't hear. You can't even breathe. There's ash everywhere."
His neighbor, Brian Smith, a motion picture grip who has lived in Canyon Country since 1981, patted the side of his white recreational vehicle.
"I guess," he said, "we could live here."
By early this morning, about 60 people had gathered at an evacuation center opened at Saugus High School. Loretta Graham and some of her neighbors had settled into the gym, where some people sat at folding tables, quietly talking over their unexpected ordeal, while others, exhausted, slept on cots in the darkened part of the cavernous room. The mood was relaxed, if somewhat subdued. About another 40 people were sleeping in their cars outside the gym.
Graham was relaxed as she chatted with her 27-year-old daughter, April Graham.
"We always try to make the best of things," Loretta said.
As of 1 a.m. today, they still didn't know the fate of their two-story home on Old Friend Road.
"I hope the house is still standing in the morning," April said of the family home of 20 years.
Along with Loretta and April, three others live at the home. There's Loretta's 13-year-old daughter, Ashleigh, and April's husband, Robert O'Brien, and their 6-year-old son, Max.
In the moments before they were forced to flee Sunday, Loretta took the family dog and April retrieved important photo albums and family documents. "Whatever I could grab in two minutes," April said.
Her mother added, "We're counting our blessings that everybody got out safe."
While Loretta and April chatted, their children slept on cots. April, referring to her son, Max, said, "I think he thinks he's camping."
"There is a lot of kindness here," Loretta said. "The volunteers are very doting upon us, making sure we have everything we need."
Scanning around the room, April noted that there seemed to be as many volunteers as evacuees. "They gave my son a teddy bear," she said.