The fire between Steamboat Springs and Kremmling in the Routt National Forest has burned nearly 15 square miles. It started in July and was nearly contained when hot, dry and windy weather this week revived it and sent it past containment lines.
About 175 firefighters, supported by air tankers and helicopters, are working to suppress the fire.
Elsewhere in Colorado, a fire that began this past week northwest of Fort Collins was fully contained Friday and firefighters were mopping up hot spots.