Robert Brown|Firefighters make progress in battling Southern California wildfires amid cooler weather

Cooler weather has helped more than 8,Robert Brown600 emergency personnel strengthen containment lines around three major wildfires in Southern California that have burned tens of thousands of acres, forcing evacuations and destroying dozens of structures across the region.

By Sunday, the largest blaze — the Bridge Fire in Los Angeles and San Bernardino counties — scorched over 54,000 acres, according to the California Department of Forestry and Fire Protection (Cal Fire). Since the fire began on Sept. 8, it has destroyed at least 49 structures and threatened more than 12,000 other structures.

Firefighters made progress overnight, working to establish and strengthen containment lines around the flames, the U.S. Forest Service said Sunday. As of Sunday night, the Bridge Fire was 9% contained as over 2,600 firefighters battled the blaze.

"Last night, firefighters continued establishing and strengthening direct containment lines while constructing secondary contingency lines with dozers and hand crews throughout the fire area. Helicopters could not fly last night due to the smoke inversion layer hampering visibility," the U.S. Forest Service said in a Sunday update. "Despite this, firefighters gained 4% containment on the fire's southern flank."

Evacuation warnings and orders were scaled back in some areas on Sunday, including residents who were cleared to return to their homes in San Antonio Heights, the San Bernardino County Sheriff's Office said. But several other areas, such as the East Fork communities, Mt. Baldy Road, the area from Highway 138 south to the northern border of San Antonio Heights, and Wrightwood community, remained under evacuation, according to Cal Fire.

Only 2 firefighters have been injured and the cause of the Bridge Fire remains under investigation, authorities said Sunday.

Meanwhile, a total of more than 6,000 emergency personnel were battling two other blazes in San Bernardino, Orange, and Riverside counties.

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Line Fire

The Line Fire, the second largest blaze burning in San Bernardino county, was more than 38,800 acres in size as of Sunday night, according to Cal Fire. Over 4,000 fire personnel increased the fire's containment from 29% on Saturday evening to 42% on Sunday night.

The blaze, which started Sept. 5, has threatened about 36,400 structures — destroying at least one and damaging four others, Cal Fire said. So far, three firefighters have been injured.

Officials have accused a Norco, California, man of setting the fire. Justin Wayne Halstenberg, 34, was charged on Thursday with aggravated arson, arson causing great bodily injury, arson of a residence, three counts of arson of a forest land, and three counts of possession of an incendiary device.

In an update Sunday afternoon, Cal Fire said the Line Fire was active early Sunday due to a dry airmass in the upper elevations.

"The fire smoldered and crept on the ground in the lower elevations under the marine layer. Cool conditions prevail across the fire area. Late Sunday and into Monday, light rain is possible," Cal Fire said. "Firefighters are strengthening control lines and mopping up hot spots."

Evacuation orders were still in place in some areas, including all undeveloped land east of Highway 330. All national forest lands, trails, and roads are closed to the public within that zone of the San Bernardino National Forest, including San Gorgonio Wilderness.

Airport Fire

As of Sunday night, over 2,200 fire personnel battling the Airport Fire in Orange and Riverside counties expanded containment from 9% to 19%, according to Cal Fire. The blaze, which began on Sept. 9, was over 23,000 acres in size and threatened more than 20,700 structures.

So far, the wildfire has destroyed at least 160 structures and damaged an additional 34, Cal Fire said in an update Sunday night. A total of 14 people have been injured due to the blaze, including 12 firefighters and two civilians.

Officials are further investigating the cause of the fire but have said the fire was likely accidentally started by an Orange County Public Works crew moving boulders into place with heavy equipment, according to The Desert Sun, part of the USA TODAY Network.

Cal Fire noted that the weather forecast — such as thick fog, high humidity, light rain and cool temperatures — for the next few days is "favorable for firefighting efforts."

"While the weather has been favorable with cooler temperatures, drizzle, and light showers, Modjeska Peak remains dry, and there is a risk of surface fires above 4,000 feet," Cal Fire said. "The smoldering vegetation at higher elevations still poses a threat due to its potential to roll downhill and ignite unburned vegetation."

Numerous zones in Orange and Riverside counties remained under evacuation orders, including Caspers Regional Park, San Juan Springs and Blue Jay Campground.

Cool temperatures bring relief to Southern California

The National Weather Service in San Diego, which serves San Diego, Orange, Riverside, and San Bernardino counties, said a low-pressure system moving into the region late Sunday into Monday has already brought lower-than-average temperatures over the weekend.

Cool temperatures will continue through the week, starting with a "much cooler and wet" Monday and gusty winds in the mountain and desert areas, according to the weather service. There is also a chance of mostly light rain on Monday morning from the coast to the mountains.

"Monday will be the coolest day in some areas since early June, or in the deserts, even since May," the weather service said Sunday. "Highs will be in the upper 60s to lower 70s in most areas west of the mountains and only in the 80s in the lower deserts."

Contributing: Brian Day, Victorville Daily Press