Dry lightning from a quick moving thunderstorm ignited the fires around 4:30 p.m. Wednesday.
Within four hours, the Humboldt fire was about 250 acres and the Lookout fire was around 20 acres, said forest spokesman Dave Killebrew.
He said crews did emergency burnout operations around the FAA site and lookout tower to rid the area of fuel as flames approached the top of the mountain where the structures were located.
The two fires were burning within a mile of each other and ``there is a chance that the two fires could burn together sometime during the evening,'' Killebrew said. ``The threat has not gone away.''
But late Wednesday night, forest dispatcher Allen Cross said there had been no damage to either the FAA site or the lookout tower.
Killebrew said the wind-driven fires were burning desert vegetation and were about seven miles north of the Cave Creek and Carefree communities, but no other structures were immediately threatened.
The FAA site is one of several that provide communication for commercial air traffic. Killebrew said he was not aware of any FAA communication interruptions Wednesday.
Six engines, an air tanker and two helicopters were being used to stop the flames. One hot shot crew was working the fire and another two more elite crews were ordered.
Killebrew said firefighters would be battling the flames through the night.
