The Salmon-Challis and Bitterroot National Forests say the Chrandal Creek fire on the Idaho-Montana border is now estimated at 2,200 acres.
The lightning-caused fire was listed as 40 percent contained Monday morning. Only 70 acres of the fire are in Idaho.
High temperatures, gusty winds, and low humidity caused some increase in fire activity over the weekend.
Firefighters plan to focus their work at the head of Mine Creek. Hotshot crews are working in tandem with helicopters in steep, rugged terrain to keep the blaze from moving east.
A Stage 1 Evacuation Notification is still in effect for residents in the upper Hughes Creek, Mont., area. They could be asked to leave if a fire threat becomes imminent.