Los Angeles - California firefighters working in withering heat battled wildfires Thursday in rugged mountains above the foothill suburbs of Los Angeles, in the central coast region and on the outskirts of Yosemite National Park.

Weather plagued fire crews as temperatures in some areas rose toward triple digits and humidity levels headed downward. For a second day, the National Weather Service issued a red flag warning of extreme fire conditions for many of Califonia's central and southern mountain ranges.

No major structural losses were reported.

The major battles in Southern California were in the San Gabriel Mountains as firefighters struggled to keep flames from topping ridges and surging into a wider area of the sprawling Angeles National Forest northeast of downtown Los Angeles, where the temperature hit 99 degrees before noon.

The largest of two fires, which spread lung-burning haze over much of metropolitan Los Angeles, was 45 percent contained after burning across 1,850 acres, or nearly 3 square miles, said Capt. Jim Wilkins of the U.S. Forest Service.

Nearly 1,000 firefighters aided by bulldozers and a fleet of water- and fire retardant-dropping aircraft were concentrating on the fire's northeastern edge.

Wilkins said the area is so steep that "it's almost to the point where you need ropes" for firefighters to reach it.

The heat and very low humidity - which saps moisture from vegetation - were not helping.

"When you have all of those factors in alignment, it just burns explosively," Wilkins said.

On Wednesday, about 70 people were ordered evacuated from a trailer park and private campground along a fork of the San Gabriel River, Wilkins said.

The fire, believed caused by human action began Tuesday near a dam and reservoir in San Gabriel Canyon, a half-dozen miles above the city of Azusa.

A second fire erupted in the forest on Wednesday about 20 miles to the west, north of the foothill suburb of La Canada Flintridge.

The 30-acre fire was 20 percent contained and more firefighters and helicopters were being requested, said Forest Service spokeswoman Randi Jorgensen.

"I think they're concerned that it might travel today," she said.

In southern Monterey County, a blaze that erupted Wednesday grew to 2,754 acres, or 4.3 square miles, but evacuation orders were lifted for 20 residences in the Lockwood-Jolon area, said Curt Itson, a spokesman for the California Department of Forestry and Fire Protection.

The blaze was 60 percent contained after burning two outbuildings and a trailer.

Elsewhere in the central coast region, a wildfire that has scorched 140 square miles of brush this month in the mountains of Santa Barbara County flared up Wednesday, burning another 1,000 acres but remaining within containment lines.

The fire began on Aug. 8. Investigators said it was caused by a cooking fire set by marijuana traffickers in Los Padres National Forest.

Meanwhile, the two dozen cabins that make up the Yosemite National Park enclave of Foresta were evacuated at 1 a.m. Thursday as a wildfire closed in. The fire began as a prescribed burn and jumped its boundaries, quickly growing from a planned 90 acres to 1,170 near midday.

The fire forced closure of parts of Highway 120, the route most popular with visitors driving in from the north.