Mount Harper is a deeply eroded Late Proterozoic volcanic complex located 71 km (44 mi) north of Dawson City and 33 km (21 mi) west of Mount Gibben. Mount Harper is in the Ogilvie Mountains and is the 1,200 m (3,900 ft) thick remnant of a subaqueous-to-emergent basaltic shield volcano capped by small rhyodacitic and andesitic lava flows.