Stubborn wildfire continues in S. Calif.

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

Updated 1:52 p.m. ET

(CBS/AP) IRWINDALE, Calif. - Hundreds of firefighters are trying to control a major wildfire just outside Los Angeles.

It has burned 3,600 acres, or roughly 5 1/2 square miles. Five firefighters suffered minor injuries.

For some 12,000 outdoor enthusiasts in southern California, Labor Day wasn't what they'd expected: instead of hiking and camping - a natural farewell to summer - they had to flee the mountains in Angeles National Forest to escape the wildfire.

"It's been hot for a while now," Nathan Judy of the U.S. Forest Service told correspondent Bill Whitaker. "We know that everything is dry. We're fighting it real hard with aircraft and boots on the ground."

The fire is burning deep in the mountains, about 7 miles from the nearest communities. Currently no homes are threatened.

"Due to the steep terrain, the medium-to-heavy fuels and the moderate-to-high winds we're starting to experience in the fire area, this firefight is limited primarily to an aerial attack," said Tony Imbrenda of the Los Angeles County Fire Dept.

Four fire fighters were treated for heat problems and one for a twisted ankle. No one had to be hospitalized.

As of late Monday the fire was 5 percent contained.

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Williams Fire, Angeles National Forest: Overview (InciWeb)

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 continue to burn deeper into a wilderness area away from any structures.

The fire started Sunday near a wilderness camp and quickly grew.

"We were planning to play and have fun up there with our family and our dogs and have fun and eat and be safe," young vacationer Jose Raya told CBS News. "But now I'm not sure where to go."

Park campgrounds have been off-limits to visitors since Sunday because of firefighters' road blocks, but the fire is moving away from inhabited areas.

Many residents in a private mobile home community also were evacuated Sunday, but up to 75 residents have chosen to stay in their homes.

Firefighters say they're not sure how this fire started. They hope to have it contained by next Monday.

Just three years ago, in the very same park, the Station Fire burned more than 160,000 acres and killed two firefighters.

In Northern California, firefighters are focusing on the rugged and remote northern edge of a weeks-old fire in Mendocino County. That blaze has scorched more than 65 square miles.