The Beaver Creek fire topped 92,000 acres as of late Saturday and was only 9 percent contained as more than 700 firefighters wrestled with the rugged and heavily wooded terrain.
"You never want to trust a fire, especially this one," said Incident Cmdr. Beth Lund, adding the Beaver Creek blaze was "just an aggressively active fire."
Lund and her management team were in the process Sunday of combining the command of the Beaver Creek fire with than of the nearby McCan fire, which was declared fully contained at 23,389 acres.
The Beaver Creek blaze Sunday threatened the Ketchum area, where additional evacuations of West Ketchum were considered likely and smoke was becoming a health concern for residents, the Twin Falls (Idaho) Times-News said.
"Maintain situational awareness and be prepared to depart on short notice if conditions change again," the Blaine County Sheriff's Office advised residents in a written statement.
The National Interagency Fire Center said Idaho was the most-active front on a widespread war against wildfires throughout the West. Idaho had nine large fires totaling nearly 408,000 acres, and red-flag weather warnings were in effect in the southern half of the state.