About 450 firefighters from several agencies fought the ferocious Waldo Canyon fire 10 miles west of Colorado Springs, which charred more than 3,600 acres in about 36 hours, the U.S. Forest Service said.
Relative-humidity levels were near zero Monday, drying trees and grasses to tinderbox conditions.
Temperatures would reach 100 degrees Fahrenheit Monday and Tuesday and remain in the upper 90s during the day through Friday, AccuWeather forecast.
Rain was not due until July 2 or 3.
Temperatures hit 100 Saturday and Sunday amid strong winds.
"This is a day we've long dreaded would come," Colorado Springs Mayor Steve Bach said at a news conference Sunday afternoon.
Deer and other animals ran through Colorado Springs neighborhoods to flee the fire, residents told The (Colorado Springs) Gazette.
As many as 2,300 city residents were evacuated.
More than 11,000 people were originally evacuated from communities near Pikes Peak, a 14,115-foot mountain in the Front Range of the Rocky Mountains.
About 5,000 of the 6,000 people living in Manitou Springs, at the base of Pikes Peak, were allowed to return home beginning at 8 p.m. Sunday.
The fire earlier pushed to within a quarter-mile of Manitou Springs.
Mandatory evacuations remained in place for the nearby communities of Cascade, Green Mountain Falls and Chipita Park, officials said.
The 19-mile Pikes Peak Highway was closed Monday, as were a number of parks, including the 3,300-acre Garden of the Gods, known for towering columns of red rock.
Four specially equipped C-130 Hercules turboprop military transport planes -- capable of dropping 3,000 gallons of fire retardant in less than five seconds -- were to help with the fire starting Monday as a Type 1 incident command team, the highest classification for fire disasters, was expected to take over the fire operations.
The fire began Saturday afternoon. Officials did not immediately say if they knew what sparked it.
At least eight large fires were burning in Colorado Monday, including the High Park fire near Fort Collins, which has blacked more than 82,000 acres and destroyed at least 191 homes.
At least 19 major wildfires burned across the western United States, including one of the largest blazes in the history of New Mexico.