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A wildfire in southern Arizona is burning more land on a mountaintop community.

The fire has charred more than 12,400 acres on Mount Lemmon, which is just north of Tucson. More than 250 homes have been destroyed, and the fire is only five-percent contained Monday.

But firefighters say no more structures were lost to the blaze overnight. Firefighters are planning on digging lines ahead of the fire's northern edge.

Flames are heading into a wilderness area down one slope of the mountain, prompting the evacuation of a youth camp and two ranches.

Authorities are still investigating the cause of the blaze. They're expected to survey the fire's starting point Monday.