Fire creeps slowly down the western canyon wall above the Wood River near Hailey, Idaho, on Sunday. Fire managers expressed optimism in their battle against the Beaver Creek Fire that has scorched nearly 160 square miles and forced the evacuation of 2,300 homes near the central Idaho resort communities of Ketchum and Sun Valley.

Officials said the blaze had grown by only about 12 square miles because of cloud cover the day before and the arrival of additional crews and equipment. Many firefighters worked Sunday to create protective firebreaks, or gaps in vegetation.

“Today they’re very optimistic that we will reinforce those lines in case the fire does flare up as we saw on Thursday and Friday,” fire spokeswoman Shawna Hartman said.

More than 1,200 people and 19 aircraft were battling the lightning-caused wildfire, which started Aug. 7 and was 9 percent contained Sunday.