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 Beaver Creek Fire, which started Aug. 7 and was 9 percent contained. Nearly 90 fire engines also were in the region, many protecting homes in the affluent area where celebrities like Arnold Schwarzenegger, Tom Hanks and Bruce Willis own pricey getaways.
Hartman said Sunday retardant was being dropped on the flank of Bald Mountain - the Sun Valley Resort's primary ski hill - to reinforce a fire line. That meant the famed ski mountain known as "Baldy" and often used in publicity photos would have a red line of retardant visible from Ketchum.
Hartman said the drop was part of a plan by fire managers to bolster protection for the tony resort town, but he noted the fire had not yet spread to the mountain.
Meanwhile, crews continued battling other wildfires across the West, including a group of fires near the Oregon city of The Dalles, on the Columbia River.
Those fires were threatening about 70 homes Sunday, and some residents in the area were told to be ready to evacuate. The state fire marshal's office said there was fire about a mile and a half from some structures.
Three wildfires were burning in the area, with the largest covering about 700 acres in The Dalles watershed. The lightning-caused fires were detected Friday. About 200 people were assigned to help combat them.
In Idaho, fire managers said both of the nation's DC-10 retardant bombers have been used to battle the Beaver Creek Fire, but one experienced an engine malfunction after a drop Thursday. The jet made it back safely to Pocatello in southeastern Idaho but remains unavailable.
Hartman said most of the fire's containment was on the south and west sides. The more populated areas are on its eastern side and are where the mandatory evacuations were in place.
Blaine County spokeswoman Bronwyn Nickel said Idaho National Guard soldiers were manning checkpoints at evacuated neighborhoods and helping relieve local law enforcement officers. The Blaine County sheriff's office was warning evacuated residents not to return until notified it was safe to do so.
No structures have been destroyed since a house and outbuildings burned Thursday, officials said. On the fire line, a few minor injuries were reported.
Authorities have told Ketchum and Sun Valley residents to be ready to evacuate if necessary. About 2,700 people live in Ketchum and 1,400 in Sun Valley.
In Utah, the last evacuation orders were scheduled to be lifted Monday after a series of mountain fires burned more than a dozen homes last week.
More than 100 residents who were forced to leave Rockport Estates and Rockport Ranches, about 45 miles east of Salt Lake City, will be allowed to return in the morning, officials said.
Among them are family members of a couple who got married over the weekend in a backup ceremony at a century-old church after they had to flee their original venue with the bride's wedding dress.
Tawni Sprouce and Travis Mann planned to exchange their vows at her parents' home overlooking Rockport Reservoir. But the residence was among the scores evacuated after the lightning-sparked Rockport fire burned nearly 2,000 acres.
First, the couple moved the wedding to a campsite at Rockport State Park near the community of Waneship. But rain pushed the ceremony inside the park's Old Church.
Mann said that given the circumstances, the couple welcomed the precipitation. He said Saturday's ceremony eventually went off without a hitch.
Fire officials said Sunday the Rockport fire was 70 percent contained.
Utah's biggest blaze, the Patch Springs Fire, was estimated at 50 square miles and 25 percent contained Sunday. Evacuation orders were lifted for that fire, which burned eight to 10 homes near Willow Springs, but a portion of state Highway 199 remained closed.