The fire began around 9:30 a.m. Thursday near the fence line separating the United States and Mexico, said Ellen Brown, a fire prevention officer for the Coronado National Forest.
The fire was discovered Thursday when two Arizona Department of Corrections fire crews were on their way to help prepare a prescribed burn, said Dean McAlister, fire management officer for the Coronado National Forest.
''We were fortunate to have crews working a prescribed burn close by,'' Brown said, adding they were on the scene in minutes.
About 70 firefighters worked the blaze.
It was determined that an abandoned campfire caused the fire, McAlister said.
No structures were threatened by the fire, which is in a remote area south of Sierra Vista just north of the border.
