The Black Tusk is considered to be the remnant of an extinct andesitic stratovolcano which formed between about 1.3 and 1.1 million years ago. Following glacial dissection, renewed volcanism produced the lava dome and flow forming its summit about 170,000 years ago. According to Natural Resources Canada, The Black Tusk was perhaps the conduit for lava within a cinder-rich volcano. The loose cinder has eroded, leaving only the hard lava core. The exposed lava rock of the core is loose and friable. It is also black, giving the mountain its name and character. Cinder Cone, to the east of The Black Tusk, produced a long lava flow during the late Pleistocene or early Holocene.