LOS ANGELES — Helped by cooler temperatures, firefighters gained ground Friday against three blazes in Southern California and authorities began scaling back evacuation orders that displaced thousands of people.

The largest is the Bridge Fire east of Los Angeles, which has burned 81 square miles (210 square kilometers), torched at least 33 homes and six cabins and forced the evacuation of 10,000 people. The cause of the fire is not yet known. After days of burning without fire crews being able to stop its forward march, it was 3% contained on Friday.

“Firefighters made great progress on the ground, aided by aircraft to attack the fire aggressively 24 hours per day,” the California Department of Forestry and Fire Protection said in a statement.

While firefighters have made significant progress, the three major wildfires that have ravaged the mountains east of Los Angeles, destroying dozens of homes, injuring a dozen people, and burning more than 155 square miles (400 square kilometers), still pose significant threats to some communities.

California is entering the height of wildfire season and has already seen nearly three times as much acreage burn as during all of 2023.

Evacuation orders were being scaled back, including in parts of Big Bear where the Line Fire forced thousands of people to flee. Authorities say a delivery driver purposely started the blaze Sept. 5.

The fire has charred 59 square miles (153 square kilometers) in the San Bernardino mountains, where Southern Californians ski in the winter and mountain bike in the summer. It was 21% contained as of Friday.

The Line Fire is burning through dense vegetation that grew after two back-to-back wet winters when snowstorms broke tree branches, leaving behind a lot of “dead and down fuel,” Cal Fire Operations Section Chief Jed Gaines said.

The Big Bear Zoo said it moved all its animals to a zoo in the city of Palm Desert to protect them from the wildfires and escalating temperatures.

The fires have threatened tens of thousands of homes and other structures across Southern California since they escalated during a triple-digit heat wave.

Cooler weather that began midweek has helped firefighters slowly gain the upper hand in battling the blazes. No deaths have been reported, but at least a dozen people, mainly firefighters, have been treated for injuries, mostly heat-related, authorities said.

Jason Anderson, district attorney for San Bernardino County, said Thursday that nine arson-related charges have been filed against Justin Wayne Halstenberg, who is accused of starting the Line Fire.

Anderson said Halstenberg, 34, attempted to start three fires within an hour in the city of Highland. Two were extinguished by firefighters and a good Samaritan, and the third became the Line Fire, according to authorities.

“This is particularly galling in a community that unfortunately over the last couple of years has dealt with the scourge of wildfires,” he told reporters, adding that the suspect’s vehicle has been linked to three areas where the fires were started.

Halstenberg is due to be arraigned on Monday according to the San Bernardino County District Attorney’s Office, which said Friday that it did not have information about an attorney for him.

Halstenberg’s mother, Connie Halstenberg, told the Los Angeles Times that her son “did not light that fire.”

The full extent of the damage caused by the wildfires remains unclear, but Anderson said at least one home has been destroyed by the blaze.

Farther south, the Aiport Fire in Orange and Riverside counties has burned more than 37 square miles (96 square kilometers). Reportedly sparked by workers using heavy equipment, it was 8% contained as of Friday morning.

Ten firefighters and two residents were injured in the blaze, according to the Orange County Fire Authority. The fire has been difficult to tame because of the steep terrain and dry conditions — and because some areas hadn’t burned in decades. It destroyed at least 27 cabins in the Holy Jim Canyon area, authorities said.

In northern Nevada, Washoe County officials confirmed Friday that a wildfire that broke out south of Reno last weekend destroyed 14 homes the first two days but none since as containment continues to increase.

Authorities have lifted all but a few of the evacuation orders that initially forced covered as many as 20,000 residents. Power has been restored to all but about 140 customers, NV Energy said. No deaths or serious injuries were reported.

Containment of the Davis fire was estimated at 56%, with no growth in the perimeter for the third day in a row after it burned nearly 9 square miles (23 square kilometers) of timber and brush along the Sierra’ Nevada’s eastern slope near Lake Tahoe.

The Washoe County sheriff was seeking tips from the public as an investigation continued into the origin of the human-caused fire, which started Sept. 7 in a regional park about halfway between Reno and Carson City.