Mahogany Mountain is the eroded remnant of an ancient caldera volcano in the Owyhee Mountains on the Oregon-Idaho border, within the Basin and Range Province. Its last eruption likely occurred about 15.5 million years ago during the Miocene, when intense regional volcanism spread rhyolite, tuff, and ash across the area and helped form nearby features such as Three Fingers and Castle Peak. Erosion later carved the volcano into a narrow, ridge-like caldera with steep slopes and a prominent northwest escarpment. Leslie Gulch exposes striking volcanic layers within the depression, and the nearby Owyhee River supported Native American fishing, hunting, and camping long before European settlement.