Bald Mountain is the economic driver for the Wood River Valley, drawing more than 400,000 skiers each year to Sun Valley. But forest managers say the health of the mountain’s trees is at risk. Last year, the U.S. Forest Service finalized a plan to treat more than 6,000 diseased and insect-infested acres on the mountain in the next decade. Most of the trees are Douglas firs, and they’re infected by dwarf mistletoe and bark beetles.