The first volcanic activity in the Northern Cordilleran Volcanic Province 20 million years ago was infrequent, creating small amounts of volcanic material. This infrequent volcanic activity was interrupted when considerable volcanism began to form the large Level Mountain shield volcano 15 million years ago. The shield volcano forms a broad cliff-bounded lava plateau long and wide, with an average thickness of . Ropy pāhoehoe lava flows predominate over blocky ʻaʻā lava flows, breccias and tuffs, attesting to a fluid and effusive character for the volcanism.