LOS ANGELES (CBS/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.

Firefighters working amid sweltering conditions in steep terrain were aided by a fleet of water-dropping aircraft in attacking flames in the mountainous wilderness about 90 miles east of Los Angeles.

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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.

Nearly 1,900 firefighters were working the fire. None had been reported injured since the flames 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 stalled over the region. Mountain temperatures were predicted to range from 90 degrees at 6,000-foot elevations to 100 degrees at 3,000 feet. Humidity levels were low, which makes vegetation easier to burn.

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, where air-quality levels reached unhealthy levels Friday, the South Coast Air Quality Management District said.

The fire could eventually reach the desert, said Lyn Sieliet, a U.S. Forest Service fire spokeswoman. Ten fire engines and a bulldozer were sent to patrol the Morongo Valley and Pioneertown areas at the east end of the mountain range.

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The fire was not threatening Big Bear Lake, a year-round mountain resort destination to the north of the fire.

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

A blaze burned more than 1,000 acres near San Luis Obispo. (CBS)

A blaze burned more than 1,000 acres near San Luis Obispo. (CBS)

A blaze that burned at least two homes near Santa Margarita, just northeast of San Luis Obispo, grew to about 1.8 square miles. Helicopters were taking water from nearby Santa Margarita Lake to dump on the blaze, which was 15 percent contained.

Several hundred residents were evacuated at the height of the fire Saturday afternoon, the San Luis Obispo Tribune reported.

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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