No houses were immediately threatened as prevailing cooler weather, lighter winds and higher humidity helped reduce the spread of flames.
"It's pretty slow," U.S. Forest Service spokeswoman Lisa Duke said of the 2,500-acre Pinnacles Fire in San Bernardino National Forest.
The fire was burning northeast of the city of Lake Arrowhead, about 80 miles east of Los Angeles.
It was 10 percent contained after flames closed Highway 173. Two firefighters were injured when a Bureau of Land Management water truck overturned. Their injuries were not considered life-threatening.
The fire was moving into an area overgrown with dry grass and brush. It would have to cross a ravine and creek then travel several miles before reaching hundreds of homes.
Officials recommended voluntary evacuation of some nearby high desert communities, including a section of Apple Valley.
Another fire was burning 10 miles north of La Canada Flintridge in Angeles National Forest north of Los Angeles.
Dubbed the Pines Fire, it was 40 percent contained after burning 150 acres and prompting authorities to close a portion of Angeles Crest Highway, forest spokeswoman Kathy Peterson.
No homes were threatened, but a fire station, school and outdoor education center were closed.
"The fire has laid down," Peterson said. "If the weather changes, it gets hot, winds pick up, it could change in a heartbeat."
In Ventura County, a stubborn fire in Los Padres National Forest that began on Labor Day was 20 percent contained. It has scorched 97,685 acres, or nearly 153 square miles in an area 75 miles northwest of Los Angeles.
The town of Lockwood Valley, about seven miles from the edge of the fire, remained under voluntary evacuation.
"We're not seeing any extreme fire behavior," said Larry Comerford of the U.S. Forest Service.
More than 2,000 firefighters and 34 aircraft were fighting the blaze, with many concentrated on its active, northeastern end. They worked to carve 59 miles of firebreak before the possible return Friday of Santa Ana winds.
The fire nearly doubled in size when gusty winds blew through last weekend.
Sparked by someone burning debris, the blaze has cost $21.8 million to fight, Comerford said.
The Ventura County Board of Supervisors declared a state of emergency as the first step toward obtaining state and federal funds to ease the cost of fighting the blaze.
County Fire Chief Bob Roper estimated it could burn for another two weeks.
Authorities were beginning to worry about winter flooding in the huge swath of land denuded by the fire.
"People have to understand that hot fire glazes the soil, and water doesn't penetrate it very well when it rains," Roper said.