Mystery Mountain is a 9,830-foot summit in central Idaho's Sawtooth Range, west of Stanley, within the Sawtooth Wilderness and Sawtooth National Forest. Visible from Highway 21 and Stanley Lake, it is a prominent wilderness landmark despite lacking official adoption by the United States Board on Geographic Names. Part of the Rocky Mountains, it rises sharply above the surrounding terrain, with the summit standing more than 3,000 feet above Crooked Creek within a horizontal mile. Its waters drain toward the Salmon River through Crooked Creek and Valley Creek. The mountain lies in an alpine subarctic climate marked by long, snowy winters and cool to warm summers.