Pioneer Mountain is a 10,525-foot peak in Idaho’s Pioneer Mountains, standing on the border of Blaine and Custer counties and marking the boundary between the Sawtooth and Salmon-Challis national forests. Its topographic isolation is 1.47 miles. The mountain also divides two drainage systems: water from its southern and western slopes flows through tributaries of Muldoon Creek to the Little Wood River, while runoff from its northern and eastern sides reaches tributaries of Star Hope Creek within the Big Lost River watershed.