Two casinos and a high school were opened as evacuation centers for residents.

Ron Lane, San Diego County’s deputy chief administrative officer, said a large portion of a mobile home park had been destroyed, along with other houses in the Bonsall area. He said more evacuations would be ordered Thursday night, and urged people to prepare to leave their homes.

“This is a very dangerous period of time we’re going through in the County of San Diego over the next 24, 48 hours,” Mr. Lane said. “We have to be resilient.”

Brian Jones, a concrete contractor from Bonsall, went to the Del Mar Fairgrounds on Thursday night to drop off his three horses. Mr. Jones, 58, has had to evacuate his home in the past, and he said he had spent several hours wondering whether to do it again.

“I didn’t want to leave,” Mr. Jones said. And then the flames “started coming over the ridge, right at the edge of our development, and it was ‘Oh, boy — time to go.’”

A fire erupts in Riverside County.

State and local officials said the fire near Murrieta, in Riverside County, east of Los Angeles, continued to grow on Thursday, reaching 300 acres by late afternoon. One structure was destroyed, officials said, and the fire was 5 percent contained.

County officials said the brush fire was “burning at a moderate to rapid rate of spread” in an area of “heavy fuels.” Evacuations were ordered in some areas, and about 300 firefighters from several departments were at the scene.

Residents are evacuating as Ojai is ringed by flames.

Ojai, a mountain-fringed town known for its unique shops and yoga retreats, was among the areas evacuated in Ventura County, where a fire had burned 115,000 acres by late Thursday with only 5 percent containment.

“We’ve always been under threat of fire; we’re used to it,” said Suzanne White, who drove past curtains of flames above the 101 freeway as she fled her Ojai home. “But this year, the fires are raging so fast and furiously that you can’t get ahead of them.”

The state firefighting agency said Thursday that “significant fire growth” had been reported north of Ojai, and the state’s fire map showed the community virtually surrounded.

Ojai, population 7,500, was among several cities threatened in Ventura County, where more than 400 buildings had been destroyed as of Thursday night and 85 more damaged. Around 15,000 more structures were threatened, and about 2,500 firefighters were assisting.

“It burns,” Ms. White said, “and it keeps burning.”

Part of the region’s 101 freeway was shut down Thursday morning as the fire reached the highway and edged northwest of Ventura.

“The entire town slept with one eye open,” a Ventura resident, Tracie Fickenscher, said.

Read more from people who were at the front lines of the fires here.

The horses were much calmer than their owners.

With flakes of ash the size of flower petals falling along the Pacific Ocean, Brian Holt, 55, paused along a coastal road on Thursday afternoon to take a picture of the smoke-blackened skies.

Mr. Holt has spent the last four days shuttling horses to safety from ranches threatened by the fire in Ventura County. He drove the animals through canyons filled with flame. “You could feel the heat,” he said. “I had to check my truck to make sure the paint hadn’t bubbled.”

The horses, he said, had been much calmer than their panicked owners. “For some of those folks the horses are their children,” he said.

He had been surviving on catnaps since Sunday. “This one is the worst I’ve ever seen,” he said. “You had to load up and go.”

A ‘miraculous result’ in Los Angeles, but warnings of danger still to come.

The fire in Bel-Air was only 30 percent contained, but it had only destroyed six structures and damaged 12 others, which the area’s City Council member, Paul Koretz, called “almost a miraculous result.”

“Nothing jumped the freeway, which is one of our greatest concerns,” he said. “Everything went as well as it could.”

Fire trucks from all over the state — Alameda County in the Bay Area, Riverside County to the east — lined the neighborhood’s narrow streets, joined by several crews from the California Department of Corrections and Rehabilitation.

Hugh Seligman, 71, returned to his intact home on Thursday, though it remained under an evacuation order.

“I would rather be here and be vigilant myself and get these guys to help if I need it,” he said. “I’ve spoken to loads of firefighters and nobody has told me I can’t be here.”

The thick smoke that smothered west Los Angeles on Wednesday had almost completely dissipated. As people in Ventura and Santa Barbara Counties, and parts of the San Fernando Valley, made their way through a choking, gray-brown haze, many Los Angeles residents were treated to a cloudless blue sky.

Along the 405 freeway, which had been shut down for part of the morning commute Wednesday, cars moved even more quickly than the usual crawl.

But in west Los Angeles, as in other communities, officials were not declaring victory, insisting instead on the need to remain vigilant and watch the weather.

Mr. Hogan, the assistant city fire chief, said, “In a wind-driven event, wind is king.”