A wildfire northeast of Los Angeles spoiled the Labor Day plans of thousands of visitors to the Angeles National Forest as firefighters bore down Monday (Sept. 3) for what figured to be a long fight against the big blaze.

A day after the wildfire broke out near a campground and forced the evacuation of thousands of campers and picnickers, it had grown to more than 4,100 acres, or roughly 6 square miles, and was just 5 percent contained, the San Francisco Chronicle reported.

Officials set up an incident management team early Monday to map out a long-term strategy to battle the blaze, U.S. Forest Service spokeswoman Angie Lavell said.

Only light winds were blowing in the area, and the flames continued to burn deep in a wilderness area away from any structures.

Campgrounds that attract up to 12,000 visitors on the holiday weekend, as well as rehabilitation centers and the private community of Camp Williams Resort, were evacuated Sunday.

The Red Cross set up an evacuation center at Glendora High School.

The forest is heavily used by Southern California residents because it is close to populated areas.

Officials said campgrounds, while not in the line of the fire, had to be emptied so that the only road in and out of the San Gabriel Canyon could be open just for fire trucks and emergency vehicles.

About 300 firefighters were aided by six water-dropping helicopters, an air tanker and 25 engines. Fire officials activated the use of a DC-10 capable of dropping thousands of gallons of retardant.

The cause of the fire was under investigation.

Another wildfire broke out Sunday in Ventura County in the Los Padres National Forest. Firefighters stopped its growth after it burned about 30 acres.