Updated

Firefighters launched a fleet of seven retardant-dropping airplanes against Southern California's latest destructive wildfire on Friday.

The blaze has destroyed 26 homes and threatened more than 500 others in the San Jacinto Mountains. Fire officials say the blaze was 40 percent contained Friday night.

The so-called Silver Fire has forced some 1,800 people to flee their homes and injured six people, including one civilian with serious burns. The fire had grown by 3,500 acres to 27 square miles by late Friday afternoon, but it was showing little more than white smoke.

So far this year, California fire officials have battled 4,300 wildfires, a stark increase from the yearly average of nearly 3,000 they faced from 2008 to 2012. It's still weeks before the fire-fanning Santa Ana winds usually arrive in Southern California.

Authorities still have not determined what caused the fire.

Evacuation orders were issued in five towns. Flames were marching toward the hardscrabble town of Cabazon, where hundreds scrambled to leave in the pre-dawn hours Thursday as the mountain ridge behind their homes glowed red.

Many returned after sunrise to pack up more belongings and watch the flickering line of fire snaking along the brown, scrubby mountains.

Linda Walls, 62, sat with her family in lawn chairs and watched fire crews scrambling to douse the flames marching toward her modest home less than a quarter mile away. An American flag flapped in the gusty wind that kicked up the fire. She wiped her brow, feeling the scorching heat.

Gray and pink-tinted clouds billowed across the otherwise crystal blue sky. Neighbors could be heard coughing as they filled the beds of pickup trucks with motocross bikes, boxes of clothing, toys and packaged food.

"It seems to be taking off now," she said as sirens whirred by. "All you see are the firemen inside the blaze."

At the end of her street, a group of ostriches paced in their cages as the hill above them burned. A firefighter rushing by said they would do what they can to protect them. Nearby another pen was filled with goats.

In the nearby town of Banning, Lili Arroyo, 83, left with only her pet cockatiel, Tootsie, in its cage and a bag of important papers from her home, which was rebuilt after being destroyed in a 2006 wildfire.

"The smoke was so bad you couldn't see," said Arroyo, who lives in the town of Banning. "There were embers and ash coming down all over the sky. The smoke was really thick. I was starting not to be able to breathe."

Evacuation orders covered an RV resort called the Silent Valley Club, the rural communities of Poppet Flats, Twin Pines, Edna Valley and Vista Grande, portions of the city of Cabazon along Interstate 10, and a camping area known as Black Mountain.

A veteran of many evacuations, Dana Wright, 43, wiped away a tear as she entered a shelter at a Beaumont school and went with her family to watch TV news. She had no idea whether her Poppet Flats home of 11 years had survived. Friends said a nearby home had burned.

She and her husband hoped to find a way back up into the mountains. "I just want to look to see if we have a house," she said.

Most of Southern California's severe wildfires are associated with Santa Ana winds caused by high pressure over the West that sends a clockwise flow of air rushing down into the region.

This week's fire, however, was being fanned by a counter-clockwise flow around a low pressure area over northwest California.

It was the second major wildfire in the San Jacinto Mountains this summer. A blaze that erupted in mid-July spread over 43 square miles on peaks above Palm Springs, burned seven homes and forced 6,000 people out of Idyllwild and neighboring towns.

The latest fire also burned in the footprint of the notorious Esperanza Fire, a 2006, wind-driven inferno that overran a U.S. Forest Service engine crew. All five crew members died. A man was convicted of setting the fire and sentenced to death.

After touring the area, U.S. Sen. Barbara Boxer, D-Calif., who lives in Riverside County, said 165,000 acres have burned in California this year and climate change is setting conditions for more disastrous blazes, while budget cuts are limiting resources to fight them.

"Unless we take action, things are only going to get worse," she said.

A different blaze, a 60-acre wildfire, near Wrightwood in the San Gabriel Mountains forced evacuations of about 75 homes in several mountain communities Thursday afternoon.

The fire broke out around noon, and firefighters struggled to beat back flames in steep terrain. Homes along several winding mountain roads were being evacuated.

Wrightwood is a mountain community popular with skiers located about 40 miles northeast of downtown Los Angeles.