Firefighters tried to hold back a massive wildfire from consuming thousands of homes and a communications center in California’s Los Angeles County today (Aug. 31) as they mourned two firefighters killed when their vehicle rolled down a mountain side.

About 12,000 homes, as well as crucial communications and astronomy centers atop Mount Wilson, were threatened by fire. On the blaze’s northwestern front, two firefighters were killed Sunday on Mount Gleason near the city of Acton, according to the Associated Press.

“We ask for your understanding, for your patience as we move through this difficult time, and please, prayers for the families of our two brothers that we lost,” county Deputy Fire Chief Mike Bryant said through tears at a Sunday press conference.

Fire Capt. Tedmund Hall, 47, of San Bernardino County, and firefighter Specialist Arnaldo “Arnie” Quinones, 35, of Palmdale, were killed in the crash, the department said in a statement. Authorities did not give a cause for the crash.

The blaze was only about 5% contained late Sunday and had scorched 71 square miles in the Angeles National Forest. Mandatory evacuations were in effect for neighborhoods in Glendale, Pasadena and other smoke-choked cities and towns north of Los Angeles. At least 18 homes were destroyed in the fire and firefighters expected to find many more, authorities said.

On Mount Wilson, crews cleared brush and sprayed retardant in an attempt to ward off flames approaching the transmitters of more than 20 television stations, many radio stations and cell phone providers, said U.S. Forest Service Capt. Mike Dietrich.

Two giant telescopes and several multimillion-dollar university programs are housed in the century-old Mount Wilson Observatory. The complex of buildings is both a historic landmark and a thriving modern center for astronomy.

The fire has been growing steadily, doubling in size on Sunday. Dietrich said it was possible it would double in size yet again over the next few days.

A slight dip in temperatures was expected today, but temperatures in the 90s and low humidity would remain the norm.

The fire was the largest of many burning up and down California, including a blaze northeast of Sacramento that destroyed 60 structures, many of them homes in the town of Auburn, location of the home office of the California Association of RV Parks and Campgrounds (CalARVC). The fire had wiped out an entire cul-de-sac, leaving only smoldering ruins, a handful of chimneys and burnt cars.

The fire had blackened 275 acres amid high winds and was 50% contained Sunday night, CalFire spokesman Daniel Berlant. The governor declared a state of emergency in the Sierra foothills area because of the fire, which began Sunday afternoon.

In Mariposa County, a nearly 7-square-mile fire burned in Yosemite National Park and forced the evacuation of about 50 homes. The blaze was 50% contained Sunday, said park spokeswoman Vickie Mates. Two people suffered minor injuries, she said.

Hot, dry and windy conditions also helped fan a monthlong wildfire in rural Utah, where residents in the town of New Harmony were told to leave their homes as the blaze flared up over the weekend. The lightning-sparked fire has already destroyed three houses and blackened more than 12 square miles in the Pine Valley Wilderness area.

Meanwhile, The Gila County Sheriff’s office evacuated a subdivision and campground near a wildfire burning Sunday in the Tonto National Forest north of Payson, Ariz., according to the AP.

Authorities say the wildfire reported Sunday afternoon was burning in Ponderosa pine and had grown to 100 to 150 acres.

The blaze was burning south of the Whispering Pines subdivision and near the Water Wheel Campground.

Fire information officer Tammy Pike said she did not know how many people were evacuated.

The fire’s cause was unknown.