Mount Rainier is a stratovolcano in the Cascade Volcanic Arc that consists of lava flows, debris flows, and pyroclastic ejecta and flows. Its early volcanic deposits are estimated at more than 840,000 years old and are part of the Lily Formation (about 2.9 million to 840,000 years ago). The early deposits formed a proto-Rainier or an ancestral cone prior to the present-day cone. The present cone is more than 500,000 years old.