The Colorado blaze shrouded the state capital, Denver, some 60 miles (100km) away in smoke on Tuesday.
A woman has died in the blaze, which has burned about 43,000 acres (68 sq miles) and is still growing.
A huge fire is also burning in New Mexico - one of a total of 19 fires in nine drought-stricken western states.
The Larimer County Sheriff's Office said on Monday that one person had died in Colorado, after investigators found remains in a home that had been burned in the fire.
Although the remains have not been conclusively identified, the family of Linda Steadman, 62, has issued a statement saying she died in a cabin that she loved.
They reported her missing after the fire started on Saturday, sheriff's officials said.
President Barack Obama called the Colorado governor to offer federal personnel, equipment and emergency grants - but was unable to reach his New Mexico counterpart due to poor reception in the fire zone, the Associated Press reported.
The High Park Fire - as it has been dubbed - is still growing, with only 5% contained, reported a national incident information website..
About 118 structures have been damaged or destroyed by the blaze in Colorado - believed to have been started by lightning - and hundreds of people were forced to evacuate, officials say.