Published: Sep 07, 2010 1:49 AM EDT
Updated: Sep 06, 2010 10:49 PM EDT

DENVER (AP) - A wind-driven wildfire in the rugged Colorado foothills has spread across 4 square miles, destroying some houses and triggering evacuations of as many as 400 homes.

No injuries have been reported.

The fire broke out Monday in Four Mile Canyon northwest of Boulder.
      
Authorities couldn't say how many structures burned down, but they say at least some were houses.
      
Erratic winds gusting to 45 mph spread the flames both to the west and northeast and kept firefighting planes grounded.
      
A billowing, white plume of heavy smoke was visible for miles. The fire's cause was unknown.
      
About 200 homes scattered in and near the canyon were evacuated first. Residents of two subdivisions closer to Boulder, each with about 100 homes, were ordered to evacuate later.