The fire smoldered since a July 19 lightning strike before it erupted on Saturday on private timber land just south of Smiths Ferry.
The fire was contained late Monday at 95 acres. It was first reported at 160 acres, but subsequent aerial mapping decreased that figure, Boise Interagency Fire Center dispatchers said.
Crews from the Forest Service, Bureau of Land Management and the Southern Idaho Timber Protection Association took advantage of slightly cooler temperatures to make as much of an advance on the flames as possible ahead of predicted afternoon thunderstorms and potentially high winds.
No buildings were threatened, and officials said traffic was continuing to move freely on Idaho Highway 55 near the fire area, despite thick smoke during the early morning hours.
Firefighters were mopping up hotspots on the western and southern flanks of the fire, running hose as much as a quarter-mile to get water into the area. Three helicopters dropping from 500 to 800 gallons of water a trip pelted flare-ups along the fire's perimeter.
It was only the fourth significant fire the state has suffered so far this summer. Experts say recent rainfall and lower than usual temperatures have kept fire potential lower than originally expected. But they also said precipitation remains far short of the level needed to end the drought that is midway through its fifth year.
They also credited the heightened awareness among the public of fire danger with limiting the number of starts.