Dan Elliott

CONIFER, Colo.: Investigators on Tuesday were trying to determine whether a routine controlled burn last week, designed to minimize wildfire risk, reignited and became a stubborn mountain wildfire that forced hundreds of residents to flee their homes, destroyed at least 23 structures and may have caused the deaths of two people.

Federal agencies dispatched hundreds of firefighters and two large air tankers to tackle the 7-square-mile blaze that forced mandatory evacuations of 900 homes south of the commuter town of Conifer, about 8,200 feet up in the Rockies foothills and 25 miles southwest of downtown Denver.

Some 450 firefighters from Colorado, Idaho, Nevada and Utah were sent to assist 250 firefighters on the ground.

The fire mostly consumed grass, brush and some Ponderosa Pine tree canopies. Winds were 20 mph to 30 mph and blowing in all directions.

Denver’s tightly populated southwestern suburbs were not threatened.

County sheriff’s spokeswoman Traci Kelley said the wildfire may have sprung from a controlled burn. The Colorado State Forest Service did conduct a 35-acre burn in the region on Thursday — on land belonging to Denver’s water authority — in an ongoing effort to reduce wood fuels for fire, said forest service spokesman Ryan Lockwood.

Crews finished the effort on Friday and patrolled the 35-acre perimeter daily to ensure it was out, Lockwood said. It was during Monday’s patrol that a state forest service crew spotted the wildfire — also on Denver Water property — alerted authorities, and began fighting it, Lockwood said. It wasn’t clear if the wildfire was inside the controlled burn zone.

The Jefferson County Sheriff’s Office will determine the cause of the blaze, while the Colorado State Forest Service was conducting its own review, Lockwood said.

Stacy Chesney, a spokeswoman for Denver Water, said the agency was “trying to be proactive” to protect water supplies from soil runoff caused by deforestation.

The area has several watersheds that feed metropolitan Denver and is several miles from the location of the 2002 Hayden Fire, one of Colorado’s worst.

Protocols for controlled fires include having a certain number of people monitoring it until it is determined to be cold — meaning nothing is at risk for reigniting, said Roberta D’Amico, spokeswoman for the National Interagency Fire Center in Boise, Idaho.

Officials found a woman’s body outside a destroyed home Monday and a man’s body inside the home Tuesday, said Daniel Hatlestad of the Jefferson County Incident Management Team. A third person was missing in the fire zone, authorities said.