The Nuttall fire had been reported at 300 acres, but better mapping showed that the initial estimates were too high, said Marylee Peterson, a spokeswoman for the crew fighting the fire.
No structures were threatened.
Seven fire crews worked to build lines around the blaze because the area contains a lot of dead trees, Peterson said.
The fire burned 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.
The fire was started by lightning.