Boulder County authorities say GPS markings indicate a fire on brush and pastureland near Hygiene is actually at 600 acres, not one-thousand as earlier estimated.
Boulder County Sheriff's Commander Phil West says roads have reopened near the fire and that crews will stay overnight to make sure that the fire doesn't flare up again.
Authorities say the fire, being fanned by wind gusts up to 30 miles per hour, is about 90 percent contained.
West says no structures other than some vinyl fences have burned, but firefighters are stationed near a few isolated homes in the area to protect them from the flames.
Authorities say about 15 fire departments are on the scene.
There are no mandatory evacuations in effect, and the Boulder County Fairgrounds in Longmont have been made available for emergency lodging for livestock and horses.
The cause of the fire is still under investigation.
West says property damage has been restricted to some fences, wood piles and grasslands.
A two-mile stretch of U.S. 36 between Saint Vrain Road and Nelson Road has been closed because of a large amount of fire traffic in the area.