There were no reports of homes damaged or destroyed, but the blaze was within a quarter-mile of at least one house and within two miles of subdivisions in the area about 25 miles west of Denver.
"We're looking at steep, rocky terrain with very thick, dry fuel," fire information officer Justin Dombrowski said. "We have pretty strong winds coming from the southwest."
The National Weather Service forecast wind of 15 to 25 mph during the afternoon. On Sunday, the wind had prevented air tankers from dropping fire-retardant slurry until just before sunset.
"The only environmental factor that can help us is that it's a downslope run to the subdivisions and fire usually runs uphill," Dombrowski said.
The Jefferson County Sheriff's Office evacuated everyone within two miles of the fire Sunday, using reverse 911 to call 1,700 homes housing 2,444 people in about five subdivisions, spokesman Jim Shires said.
Roads were packed as fire trucks joined residents fleeing with household goods, memorabilia and pets. Horses, goats and llamas were taken to the Jefferson County Fairgrounds.
Rene Baty watched smoke curl three miles away and said her home at 9,500 feet was separated from the fire only by a ridge. "We had ashes in the air, and the air was 65 mph for a while. If it comes over the mountain, there's no way to stop it," she said.
Jeff Kistner, who rents a home, said he has been chased by fires as he's moved from place to place.
"I moved in January, then moved again, and now I'm going to get burned out," Kistner said.
With dry conditions through winter, more than 400 wildfires have burned about 15,600 acres in Colorado this year, according to the Rocky Mountain Area Coordinating Center of the National Interagency Fire Center.
Residents of houses in Clear Creek and Park counties also were urged to evacuate, but no figures were immediately available on the number who left.
The cause of the fire was not known. No lightning strikes had been reported in the area.
Elsewhere in Colorado, firefighters at Colorado Springs contained a 35-acre blaze near Rampart Reservoir. A camper who tried to help fight the fire was hospitalized with serious inhalation injuries, El Paso County Sheriff's Office spokesman Jim Groth said.
El Paso County authorities also said a 40-acre fire that forced the evacuation of 20 homes a day earlier appeared to have been human caused. That fire was 100 percent contained Sunday.
In central New Mexico, meanwhile, fire lines had been established around 65 percent of a 15,000-acre blaze near Mayhill, fire information officer Victoria Fox said.
"We are under a red flag warning and expecting wind gusts up to 30 mph," Fox said Monday morning. "Everything held through (Sunday) so we're hoping for the same (Monday)."
The fire had destroyed 13 homes, 27 garages or other types of buildings, and five vehicles, officials said. It was started accidentally last week by a man who later committed suicide.