DENVER — A wind-driven wildfire broke out in the rugged Colorado foothills and quickly spread across 4 square miles Monday, destroying some homes and triggering evacuations of as many as 400 others. No injuries were reported. Authorities could not say how many structures burned down, but they said at least some of them were houses. The fire started in Four Mile Canyon northwest of Boulder, and erratic winds gusting to 45 mph spread the flames both to the west and northeast. At least four roads in the area were closed, and a billowing, white plume of heavy smoke was visible for miles. The cause was unknown. "It's fast-moving. We've got a lot of wind up there," Boulder County sheriff's Cmdr. Rick Brough said. He said emergency crews were concentrating on evacuations. About 200 homes scattered in and near the canyon were evacuated earlier in the day. Brough said residents of two other subdivisions closer to Boulder, each with about 100 homes, were ordered to evacuate Monday afternoon. At least 100 buildings were threatened. One fire vehicle was destroyed, said Patrick von Keyserling, a spokesman for the Boulder County Office of Emergency Management. At least two heavy air tankers were sent to the Rocky Mountain Metropolitan Airport southeast of Boulder to help, but the winds were too strong for them to fly over the fire. "They just can't get up until the wind dies down," Brough said. The strong winds accompanied a cold front moving across the state. They weren't expected to slacken until Monday night, said Scott Entrekin, a National Weather Service meteorologist. About 100 ground crews were on the scene and 75 more were on standby, Brough said. Three evacuation centers were set up in Boulder and in the mountain village of Nederland, and at least 65 people had checked in at the three centers by mid-afternoon. A shelter for livestock was set up at the Boulder County Fairgrounds in Longmont.