It could be a week before firefighters can contain a 3,600-acre blaze in the Angeles National Forest because of high temperatures and rugged terrain in thick brush that hasn't burned in a couple of decades.
The cause of the fire that started Sunday afternoon in the San Gabriel Mountains, spoiling holiday hiking and camping plans for thousands, has not been determined.
A burned car was found in the area, but it isn't clear if it started the fire or was just destroyed by the flames, officials said.
No structures have burned and, although four injuries have been reported, no one has been hospitalized.
Campgrounds that typically attract up to 12,000 visitors on the holiday weekend, as well as rehabilitation centers and a private mobile home community of Camp Williams Resort, were evacuated Sunday. About 30 of the 75 residents of the mobile home park chose to remain with their homes.
Daniel Burress, 68, known to park residents as "Grandpa," said he has never evacuated, even when wildfires were far closer.
"I'm a Vietnam vet," Burress told the Los Angeles Times. "So this doesn't scare me at all."
Officials said campgrounds, while not in the line of the fire, had to be emptied so the only road in and out of the San Gabriel Canyon could be open just for fire trucks and emergency vehicles.
The area burned is about 5 1/2 square miles. An update was expected later in the morning after a briefing and flyover.
In Northern California, firefighters spent Monday focusing on the rugged and remote northern edge of a weeks-old fire in Mendocino County. That blaze has scorched more than 65 square miles.
At least two other fires were contained Monday shortly after they started: a 150-acre brush fire in hills between Concord and Pittsburg on Northern California and a 100-acre blaze in Fountain Springs near Porterville in Southern California.