LOS ANGELES (AP) -- Firefighters tried Monday to hold back a massive wildfire from consuming thousands of Los Angeles-area homes and a crucial communications center as they mourned two firefighters killed when their vehicle rolled down a mountain. About 12,000 homes, as well as communications and astronomy centers atop Mount Wilson, were threatened by fire. At least 6,600 homes were under mandatory evacuation orders Sunday night and over 2,500 firefighters were battling the flames. On the blaze's northwestern front, two firefighters were killed Sunday on Mount Gleason near the city of Acton.