Soot-covered, weary firefighters continued battling a 20-mile-long blaze in Colorado's foothills Thursday, frustrated by rugged terrain but getting relief from cooler weather.

Nearly 920 firefighters worked in shifts in smoke so thick it choked out the sun at times -- mindful they might have to make a run for it at a moment's notice.

At one point this week, 60- to 80-foot flames shot toward firefighter Joey Bryan of Hot Springs, Ark. "That's when you have to pull back to a safe place," he said.

The wildfire, which grew Thursday to nearly 100,000 acres, began Saturday in the Pike National Forest. It has destroyed at least 22 homes and forced extensive evacuations. About 5,400 people remained out of their homes Thursday.

The fire slowed Thursday as temperatures fell and humidity rose, but no rain was in the forecast. Despite wind gusts to 30 mph, the blaze had not advanced toward metropolitan Denver and remained about 35 miles away from the city.

That led Douglas County to lift voluntary evacuations from several small communities between the fire and Denver suburbs.

"Over the last two days the fire hasn't done much in that north-northeast section, so the areas aren't quite as threatened as we thought a few days ago," said Douglas County sheriff's spokesman Tim Moore.

Authorities are unsure of the fire's origin other than that it was human-caused. They have said it will take up to three months to contain. Colorado is in the middle of one of its worst droughts in years, resulting in bone-dry trees and brush -- the perfect fuel for wind-driven flames.

The fire, 20 miles long and 14 miles wide, winds from the foothills dotted with small mountain towns to near Denver. It has charred about 140 square miles, leaving blackened forest floors and skeletal trees.

Colorado State Forester Jim Hubbard said firefighters were pursuing a strategy of encirclement.

"We're putting firefighters all around this fire to start trying to extinguish those hot spots and get this thing under control, but you still have to deal with those shifting winds," he said.

Most residents remain supportive of firefighting efforts, but some have questioned the tactics and complained that officials have been slow to disseminate information.

"Any information you have to dig up yourself," said Mike Holmes, who lives southeast of Florissant. "We don't have a clue."

Others have complained that slurry bombers aren't being used enough and firefighters have been too slow to act.

Fire officials have said erratic wind and thick smoke have impeded some flights. Also, ground crews have had trouble reaching the blaze because it is burning in steep terrain with few access roads.

To augment aircraft dropping slurry and water, the military has activated four modified C-130 planes. Two Army battalions and a Marine battalion, totaling more than 1,500 soldiers, have also been told to prepare to join the fight.

The fire is one of at least seven burning in the state, including an 11,648-acre blaze that was 25 percent contained near Glenwood Springs, about 150 miles west of Denver.

In northeastern New Mexico, about 1,200 firefighters were working to slow a wildfire on the Philmont Scout Ranch and Carson National Forest. The blaze, which began early this month, has charred 91,000 acres and was 25 percent contained Thursday.

Another fire broke out Thursday four miles northeast of Pecos and had grown to 200 acres by evening. "It's very active -- running, spotting, torching, crowning in the ponderosa pine," said Dolores Maese, a spokeswoman for the Santa Fe National Forest.