GLENDORA, Calif. — A wildfire northeast of Los Angeles spoiled the Labor Day of thousands of visitors to the Angeles National Forest as firefighters bore down for what figured to be a long fight against the big blaze.

Picnickers hoping to spend the day in the forest Monday ran into firefighters' road blocks instead as a large swath of the forest was closed to visitors, though the fire was moving away from inhabited areas.

Victor Saldana Jr. had a cooler full of food and drinks in the back of his pickup and was headed toward the mountains before he was forced to turn around.

"I requested the day off from work, we were looking for a nice time out today," Saldana told NBC4. "It's good that the government's taking precautions, but at the same time it kind of ruins a lot of people's plans."

A day after the wildfire broke out near a campground and forced the evacuation of thousands of recreation-seekers and a few dozen residents it had grown to more than 4,100 acres, or roughly 6 square miles, and was just five percent contained.

Officials set up an incident management team early Monday morning 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 continue to burn deeper into a wilderness area away from any structures.

The forest is heavily used by Southern California residents because it is a short drive from very populated areas.

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

About 30 of the 75 residents of the mobile home park chose to remain with their homes.

Daniel Burress, a 68-year-old who is known to park residents as "grandpa," said he has never evacuated, even when wildfires were far closer.

"I'm a Vietnam vet," Burress told the Los Angeles Times. "So this doesn't scare me at all."

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

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. Forest Service firefighters stopped its growth after it burned about 30 acres.

In Northern California, firefighters spent Monday focusing on the rugged and remote northern edge of a weeks-old fire in Mendocino County. Full containment is expected by Sept. 10.

More than 1,600 firefighters continue to battle the blaze, which has scorched more than 65 square miles and remained at 58 percent contained.

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  • This Sunday, Sept. 2, 2012 photo provided by Mitchell Edwards and taken from a flight leaving Ontario International Airport shows the growing fire in the Angeles National Forest in Southern California. The wildfire has cut short the Labor Day holiday weekend for thousands of visitors who flock to the popular recreational attraction. The fire broke out near a campground Sunday afternoon and quickly grew to 3,600 acres, or about 5½ square miles. It sent a huge cloud of smoke that could be seen from the coast to the desert inland. (AP Photo/Courtesy of Mitchell Edwards)

  • In this Sunday, Sept. 2, 2012 photo, a DC-10 tanker drops fire retardant on a ridge line at fire above East Fork Rd. near Glendora, Calif., in the Angeles National Forest. The wildfire has cut short the Labor Day holiday weekend for thousands of visitors who flock to the popular recreational attraction. The fire broke out near a campground Sunday afternoon and quickly grew to 3,600 acres, or about 5½ square miles. It sent a huge cloud of smoke that could be seen from the coast to the desert inland. (AP Photo/Rick McClure)

  • In this Sunday, Sept. 2, 2012 photo, a firefighting helicopter makes a drop with a water bucket over a fire in the Angeles National Forest near Glendora, Calif. A wildfire that broke out in the Angeles National Forest has cut short the Labor Day holiday weekend for thousands of visitors who flock to the popular recreational attraction. The fire broke out near a campground Sunday afternoon and quickly grew to 3,600 acres, or about 5 1/2 square miles. It sent a huge cloud of smoke that could be seen from the coast to the desert inland. (AP Photo/Rick McClure)

  • A plume of smoke rises from the San Gabriel Canyon area of the Angeles National Forest in the San Gabriel Mountains northeast of Los Angeles on Sunday, Sept, 2, 2012. A wildfire that broke out in the Angeles National Forest on Sunday forced the evacuation of thousands of visitors and sent a huge cloud of smoke that could be seen from throughout the Los Angeles basin. (AP Photo/John Antczak)

  • A firefighting helicopter goes to refill after dropping water on a wildfire in the Angeles National Forest north of Glendora, Calif. Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A sign on San Gabriel Canyon Road warns of a street closure as firefighters fight a wildfire in the Angeles National Forest north of Glendora, Calif. Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A fire engine pulls away as firefighters fight a wildfire in the Angeles National Forest north of Glendora, Calif. Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • Firefighters look on as they fight a wildfire in the Angeles National Forest north of Glendora, Calif. Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A hand crew looks on from a burnt hillside as firefighters fight a wildfire in the Angeles National Forest north of Glendora, Calif., Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A firefighting helicopter drops water on a wildfire in the Angeles National Forest north of Glendora, Calif., Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A firefighting helicopter drops water on a wildfire in the Angeles National Forest north of Glendora, Calif. Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • Members of a ground crew look on as a firefighting helicopter drops water on a wildfire in the Angeles National Forest north of Glendora, Calif. Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A sign near homes on San Gabriel Canyon Road in Azuza, Calif. warns of closures as firefighters fight a wildfire in the Angeles National Forest on Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)

  • A firefighting helicopter drops water on a wildfire in the Angeles National Forest north of Glendora, Calif., Monday, Sept. 3, 2012. 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 five percent contained. (AP Photo/Jason Redmond)