LOS ANGELES — Firefighters today try to hold back a massive wildfire from consuming thousands of homes and a communications center in Los Angeles County 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.

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 percent 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.