A wildfire south of Boulder that forced nearly 20,000 people to flee was listed at 21% contained and most evacuations had been lifted by Sunday morning, officials with Boulder Fire-Rescue said.

The fire, which ignited Saturday, burned to within 1,000 yards (914 meters) of homes on the west end of Boulder, said Mike Smith, incident commander.

A quick initial attack “combined with all of the fuels mitigation treatments that we’ve done in this area is one of the reasons that we’ve had such great success,” Smith said Sunday.

Fire crews were also able to use aircraft to fight the fire, laying down lines of fire retardant near homes in the rolling hills south of the college town, he said.

The evacuation area was reduced late Saturday to cover about 1,700 people and 700 residences, down from about 8,000 homes earlier in the day. Fire managers will allow more people back into their homes Sunday as it becomes safe, officials said.

Work on Sunday was focused on reinforcing the fire line and making sure the fire doesn’t burn toward the city of Boulder or down toward Eldorado Canyon, Smith said. Crews were working to corral the fire into an area of rocks and snow.

The fire burned an estimated 200 acres (81 hectares) of dormant trees and dry grass not far from where a late December fire, pushed by strong winds, burned over 9 square miles (24 square kilometers) and destroyed about 1,100 homes.

Fire crews are concerned about the upcoming fire season, Smith said.

“I think this is just a sign of the way things are going to go,” he said. “We continue to work on our planning processes. We continue to work on the team building and work with our partners to make sure that we’re as dialed as we can be. We’re feeling good, but we’re a little nervous about the upcoming season.”

Saturday’s fire started around 2 p.m. and burned protected wildland near the National Center for Atmospheric Research, Boulder police said. Authorities have called it the NCAR fire and its cause is not yet known, although officials have found the spot where it was believed to have started, Smith said.

(AP)