The blaze remained about seven miles southwest of Payson by Monday night and crews did overnight burnout operations in hope of slowing down the fire.
``There have been no evacuations,'' fire spokesman Peter D'Aquanni said Monday night. ``Hopefully, it won't happen.''
About 20 structures at ranches and properties north of the fire were threatened but weren't in imminent danger, said Gary Roberts, a spokesman for the Southwest Area Incident Management Team, which was fighting the fire.
Those structures included homes, barns and sheds.
Roberts said people from one of the ranches voluntarily left the area, but they weren't evacuated.
Nearly 590 firefighters were battling the Willow fire, which was burning cypress trees, chaparral and brush in harsh terrain in the Tonto National Forest.
Five helicopters, four bulldozers and two engines also helped with firefighting efforts.
The Mazatzal Wilderness Area was closed to the public along with two nearby roads.
The Federal Emergency Management Agency approved a request for funds to help firefighting efforts Monday.
Arizona's Division of Emergency Management also sent a hazardous assessment officer to the fire Monday to help evaluate the threat.
TUCSON, Ariz. (AP) -- Two firefighting teams from Grand Canyon National Park have been brought in to battle a lightning-caused fire that has burned 150 acres in the Pinaleno Mountains.
Authorities said no structures were being threatened by the fire, which began Saturday night.
Seven fire crews worked to build lines around the blaze Monday because the area contains a lot of dead trees, said Marylee Peterson, fire information officer for the Coronado National Forest.
The fire was burning in the rugged terrain of Nuttall Canyon, which is within the Mount Graham Wilderness Study Area about six miles from the Mount Graham International Observatory.