About 120 firefighters battled a slow-moving fire on the west side of the Santa Rita Mountains east of Tubac Thursday morning.
Observers said there was lightning in the area Wednesday night.
The flames could be seen from the Tubac area both Wednesday night and before dawn Thursday.
Smoke drifted slowly northward. The flames fed on grass, mesquites, cactus and other desert vegetation.
At 10 a.m. Thursday, a U.S. Forest Service spokesperson said, there were five hot shot crews, a site crew, two helicopters, a tanker and a smaller air attack plane working the fire.
The smaller air attack plane serves as a flying observation post, directing ground crews toward hot spots.