Investigators gathered along a remote road in a blackened forest Wednesday and hunted for clues at the spot where a gigantic blaze ignited more than a week ago and quickly grew into one of the largest wildfires in Southern California history.

Deputy incident commander Carlton Joseph said the fire was "human-caused," meaning it could have been ignited by a range of scenarios, from a dropped cigarette to a spark from something like a lawn mower. Joseph says investigators have several leads and notes that lightning has been ruled out as a possible cause.

A trio of U.S. Forest Service investigators wearing black gloves spent most of the day beneath a partially burned oak tree at the bottom of a ravine, believed to be the spot where the fire started. One investigator shook soil in a can, while another used binoculars to get a closer look. They also had planted red, blue and yellow flags to signify important locations at the site.

Click to view photos of the inferno.

INTERACTIVE MAP: Follow the flames as the Station fire grows

LIVESHOTS: Human Caused?

The investigation unfolded as firefighters made more progress Wednesday against the wildfire that has ravaged the Angeles National Forest, with higher humidity and a lack of wind providing a big boost. The blaze that had burned nearly 219 square miles, or 140,150 acres, by Wednesday.

"The crews are making excellent progress based on the improved weather conditions," U.S. Forest Service incident commander Mike Dietrich said.

Firefighters have created a perimeter around 22 percent of the blaze, largely by removing brush with bulldozers and setting controlled burns. Gov. Arnold Schwarzenegger visited the fire area Wednesday and served breakfast to firefighters, scooping Cream of Wheat into paper bowls and giving them plenty of protein so "they get all pumped up for the next fight out there with those fires."

Since erupting Aug. 26, the blaze has destroyed more than five dozen homes, killed two firefighters and forced thousands of people from their homes.

Los Angeles County Sheriff Lee Baca said only 50 homes in his jurisdiction remained under mandatory evacuation Wednesday, down from 4,000 on Tuesday. He said that about 2,000 homes in the city jurisdiction were under mandatory evacuation orders.

Some people still remained at shelters, happy to be away from the fire and smoky conditions that made breathing difficult.

Melba Cordero, 42, said she and her four children arrived on Sunday after being evacuating from her Tujunga Canyon home.

"It was horrible. We had dry cough, and the kids were getting sick. The heat was intense, and the air was very poor," she said as her children, ages 12, 10, 6 and 3, played with teddy bear and coloring books given out by shelter staff.

Nevertheless, Cordero said she's been feeling anxious and stressed out about her house.

"When is it going to end? When can be go back?" she asked. "The kids have school next week. We should be getting them ready for school."

Officials also worried about the threat to a historic observatory and TV, radio and other antennas on Mount Wilson northeast of Los Angeles. But firefighters were effectively holding back the flames and keeping them from doing any major damage.

The fire also took a toll on firefighters who bunk down each night in tents at the huge fire command center. Glendale firefighter-paramedic Jack Hayes, 31, said he had not taken a day off for a week.

"You can't sleep," said Hayes, who had the beginnings of a beard and bloodshot eyes. "You're ready to go and there's always something you could be doing."

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