UPDATE, 11:10 a.m.: Authorities report more than 4,000 acres have burned in the Williams Fire, fueled by mostly dry chapparal estimated at 15-20 years old.
Six heavy air tankers, eight helicopters and 25 hand crews are working in the steep terrain, authorities said.
More coverage of the Williams Fire:
PREVIOUSLY: A new management team was preparing to take control today of the fire that has burned more than 3,600 acres in the San Gabriel Mountains above Glendora and prompted campground evacuations, forest officials said.
The fire began about 2:15 p.m. Sunday near East Fork Road at the San Gabriel Canyon, off Highway 39, Angeles National Forest spokeswoman L'Tanga Watson said.
The blaze, believed to have originated in the trailer community of Camp Williams, grew to about 3,600 acres by 8 p.m. Sunday, Watson said.
The fire was five percent contained, and darkness prevented an accurate assessment of further fire growth until daylight, when fire officials could fly over.
"There's no estimate of full containment,'' U.S. Forest Service public information officer Robert Brady said. "The fire is moving to the north-northeast toward the (Sheep Mountain) wilderness area.''
A new fire management team was expected to set up headquarters at the Santa Fe Dam Recreation Area at the San Gabriel (605) Freeway and Arrow Highway in Irwindale, Brady said.
There were no immediate threats to structures, Brady said. The Camp Williams restaurant, private camps, the Los Angeles County inmate rehabilitation camp and a ranger station could be in harm's way eventually, so they were evacuated.
There is a tract of cabins five to six miles above the fire that will be closely watched, Brady said.
There were between 300 and 400 firefighters battling the blaze from the ground--with more expected to arrive tonight--and nine air tankers and four helicopters, Brady said.
San Gabriel Canyon was closed to the public for the duration of the holiday weekend.
A command post is set up at the U.S. Forestry building, 111 North Wabash Avenue and officials were utilizing Finkbiner Park to land a firefighting helicopter used for the nighttime surveilance of the fire's progression, said
A Red Cross evacuation center has been set up at , according to Mike Parker of the Los Angeles Sheriff's Department. It is unknown at this hour how many people may be using the evacuation area.