BIG BEAR LAKE, Calif. (AP) — Summer arrived in California on Sunday with fire season in full swing, as crews knocked down dozens of small blazes throughout the state and slowed the spread of a huge forest fire that churned through old-growth timber in the San Bernardino Mountains.

Nearly 1,900 firefighters worked in sweltering conditions and steep terrain as they attacked flames in the mountainous wilderness about 90 miles east of Los Angeles.

That blaze held steady at 25 square miles and was 15 percent contained Sunday as it pushed east toward the Mojave Desert, U.S. Forest Service officials said. It broke out for unknown reasons on Wednesday near one of the many permanent camps along state Route 38.

The fire forced several hundred people to leave the camps and vacation homes.

The National Weather Service issued a heat advisory for high temperatures through Sunday evening because of a strong high-pressure system over the region. Forecasters warned of high fire danger due to the heat, low humidity and gusty afternoon and evening winds.

About 400 buildings, including old cabins, were threatened, but none were lost.

The winds pushing the fire east carried the smoke into the desert and the Coachella Valley.

The fire could eventually reach the desert, said Lyn Sieliet, a U.S. Forest Service fire spokeswoman.

Wildfires were sparking up across the state, although most areas dodged serious destruction.

A blaze that burned at least two homes near Santa Margarita, just northeast of San Luis Obispo, grew to about 2.8 square miles. Helicopters were taking water from nearby Santa Margarita Lake to dump on the blaze, which was 50 percent contained.

Residents of 72 homes were evacuated at the height of the fire Saturday afternoon, the San Luis Obispo Tribune reported. An evacuation order for them was expected to be lifted Sunday evening.

A 920-acre fire in Madera County destroyed three structures and brought the evacuation of a handful of homes. It was 35 percent contained.

Firefighters made gains against a blaze in the Sierra National Forest, south of Yosemite National Park, that burned 500 acres. The fire was 40 percent contained by Sunday morning.

Three air tankers were brought in to douse the blaze that was started by a vehicle, according to government reports. Officials warned the blaze fed by heavy, dry brush could double in size in the next few days.

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