"We'll know more once we get the crews out there working," John Bustos, with the U.S. Forest Service, said.
Grand County Sheriff Rod Johnson says there are no homes in the immediate area, but some are within a few miles.
Overnight, humidity levels didn't climb to the 40 or 50 percent range as crews were hoping, but temperatures did dip a little bit.
"This time of year, you know we get colder temperatures at night, humidity goes up, fire lays down a little bit, get a little bit of an inversion, that cold air pushing it down," Bustos said. "So, the activity died way down. We'll know more about what kind of day we'll have, say, around 10 or 11 today."
Authorities planned to complete better mapping on the fire on Monday. Investigators were out Monday to try to determine what started the fire.
The Grand County Sheriff's Department says emergency notification calls went out to residents nearby on Sunday. Crooked Creek Young Life Camp was evacuated as a precaution, and authorities say residents living near the area should be prepared to evacuate.
County Road 50 west of Highway 40 is closed. The Fort Collins Interagency Dispatch says three heavy air tankers and one helicopter battled the fire Sunday. Firefighters say the fire is moving south and east. Sheriff's department spokeswoman Jodie Kern says the U.S. Forest Service and every fire department in the county have sent people to fight the blaze.
The U.S. Forest Service says one of the big concerns is beetle kill which severely damages the trees. Officials say trees can go up in flames in an instant, and they also put firefighters at greater risk.
"We have got a lot of dead trees up there. Those are a threat not only with a fire that could move through them but you know our fire crews have to fight in those trees and they could fall down at any time," Bustos said.
The Red Cross has set up an evacuation point at Fraser Elementary.
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