Black Butte last erupted during the Pleistocene; geologists have estimated its age at 0.4, 0.5, and 1.43 ± 0.33 million years ago. The duration of the eruptions that built the volcano remains unclear, though the activity likely coincided with large-scale block faulting in the vicinity of the Metolius Springs. Black Butte has a prominent volcanic cone and is made up of mafic (rich in magnesium and iron) basaltic andesite lava. Despite having a well-preserved, symmetrical shape and an unexposed pyroclastic core, the butte has undergone moderate erosion, with shallow ravines, deep gullies on its sides, and rocks with weathering rinds. A number of cinder cones and a volcanic field also lie nearby the butte.