Smoke from the Oak Fire, burning northeast of Mt. Lemmon, was visible this afternoon from northbound Interstate 19 south of Tucson.
The fire began June 17, and is burning near the town of San Manuel. It hit heavy fuel today, which caused the smoke.
The Oak Fire has burned 3,784 acres since it began June 17, and it is 5 percent contained.
Coronado National Forest officials are allowing it to run its natural course because it is not threatening structures, according to InciWeb, an online fire information website.
It is expected to grow until monsoon rains move into Southern Arizona.