The huge forest fire that has threatened Denver for the past 10 days was sparked not by a lightning strike, nor by an errant camper, but by that most human of flammable items — a burning love letter. 

Forestry technician Terry Barton, formerly hailed as a hero for sounding the alarm about the blaze, appeared in handcuffs in federal court Monday morning and was formally charged with accidentally setting the fire. 

On June 8, Barton, 38, was patrolling the Pike National Forest southwest of Denver, enforcing a fire ban that had been put into effect because of the severe drought. 

But she broke the law herself at a deserted campsite, torching a letter from her estranged husband and dropping the burning note in a campfire ring. Instead of dying out, the flames spread out of control. 

"She attempted to suppress the fire but it grew," Assistant U.S. Attorney Bill Leone said. 

Barton, a U.S. Forest Service employee for nearly two decades, faces 10 years in prison and $250,000 in fines. 

Barton looked down as the charges against her were read in court. Her voice quavered as she told U.S. Magistrate Michael Watanabe that she understood she could be sentenced to prison. 

U.S. Attorney John Suthers asked Watanabe to keep Barton held without bail pending a preliminary hearing. 

"She would return to a community in which there is considerable hostility towards her and she could be considered a flight risk," Suthers said. 

Barton was charged with setting fire to timber in a national forest, damaging federal property and making false statements to investigators, said Leone. 

The wildfire has so far burned nearly 103,000 acres and destroyed 22 homes. 

Driven by roaring winds, the fire spread to within 10 miles of Denver's far southwestern suburbs last week. Calmer, cooler weather and higher humidity helped crews dig lines around 47 percent of the blaze Sunday, but about 5,400 people remained out of their homes. 

The air was calm Monday morning in Denver, where a light, smoky haze hung in the air. Afternoon temperatures were expected to jump into the 80s and 90s. 

The Forest Service and Barton's friends and family expressed shock that someone they knew and trusted could have set the blaze. 

"I'm shocked and with a lot of other people, in a state of disbelief," said Rick Cables, regional forester for the Rocky Mountain Region for the U.S. Forest Service. 

Barton lives in Florissant, about 60 miles southwest of Denver. The city was among the hardest hit by the blaze, and many homes were evacuated. 

"We all wanted to believe it was some fool from somewhere else. You can understand that, we don't want to believe it. That it's one of ours makes it real sad," said Jody Penny, 45, who was evacuated from Florissant Heights on Tuesday and has been staying at an inn. 

Barton initially told authorities she smelled smoke, discovered an illegal campfire and tried to put it out by throwing dirt on it. 

Investigators later determined she could not have smelled smoke from the position she reported and confronted her with unspecified forensic evidence. 

She was charged with setting fire to timber in the national forest, damaging federal property and making false statements to investigators, said Leone. 

A court hearing was scheduled for Monday in federal court in Denver. 

Barton has worked for the U.S. Forest Service for 18 years, first as a seasonal employee and then year-round. She told reporters last week that she wouldn't rest until someone was arrested for starting the illegal camp fire. 

Although some who know Barton said they were stunned and disappointed, others voiced support. 

"She was really liked by everybody, a swell person and hard worker for the Forest Service," said Joan Spigner, who runs a convenience store in Lake George, where Barton shops. 

Neighbor Mike Vial told The Gazette of Colorado Springs that Barton is a dedicated firefighter and a good person. 

"I think this was a bad situation, and she made a stupid mistake. I don't blame her for anything. It was a stress thing," Vial said. 

About 2,200 people were fighting the fire, which has cost $6.7 million so far to fight. 

Another blaze flared in southwest Colorado and had forced the evacuation of about than 860 homes by Sunday night. The latest fire had burned more than 26,000 acres in the San Juan National Forest. 

In addition to the evacuations, residents of 450 homes were told to be ready to leave. One cabin was destroyed, and fire managers were trying to determine whether others had burned. 

More than 900 firefighters battled the blaze, about 10 miles north of Durango. 

In California, a 6,500-acre blaze in the Sierra Nevada destroyed two homes in the resort town of Walker, forced hundreds of people to flee and shut down U.S. Highway 395 south of Reno, Nev. It was only 7 percent contained by late Sunday. 

A 3,500-acre fire near Lake Isabella, 120 miles northeast of Los Angeles, had destroyed five homes, five vehicles and seven outbuildings, and briefly forced about 200 people to flee during the weekend. Officials said it was nearly half surrounded by Monday morning. 

A fast-moving Southern California fire had burned 3,500 acres of rugged forest land and temporarily closed Interstate 15 in San Bernardino. The fire jumped the freeway at least twice, and was only 10 percent contained by early Monday, authorities said. 

Higher humidity and slightly cooler temperatures helped crews battling fires in northern New Mexico. The state's largest blaze, which has charred 92,500 acres on the Philmont Scout Ranch, was 75 percent contained and full containment was expected Wednesday. 

On the East Coast, a forest fire near Myrtle Beach, S.C., had burned about 1,000 acres by Monday morning and forced 100 residents and visitors to leave a golf resort near the shore. No injuries or damage to homes had been reported. 

The Associated Press contributed to this report.