The Galena fire was burning outside Lory State Park northwest of Fort Collins, the Larimer County Sheriff's Office said.
The Denver Post reported the wildfire, originally called the Soldier Canyon fire, was being pushed by erratic winds, and efforts to contain it were complicated by low humidity and record temperatures.
"Winds have been extremely erratic," Capt. Patrick Love of the Poudre Fire Authority said.
The newspaper reported officials said Friday afternoon they had sent out 860 evacuation phone calls. Initially, 281 calls were made to the north of the fire, but concern for that area was scaled back and a second round of 579 calls were made south of the fire, the Post said.
Dozens of firefighters were deployed to battle the fire, which was first reported at 11:45 a.m. local time. Aircraft could not be used because of high winds.
A second, smaller fire reported Friday in LaPorte was contained Friday afternoon after about 50 homes were evacuated.