BOULDER, Colo.—A wildfire south of Boulder that forced nearly 20,000 people to flee was listed at 21 percent 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 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 …