Mount Funagata is an active stratovolcano formed from the end of the Tertiary period to the beginning of the Quaternary when the Ōu Mountains were raised from the sea. Mount Izumigatake is the oldest peak, created around 1.2 million years ago. The current main mountain body was completed by repeated volcanic activity from 600,000 to 850,000 years ago. Mount Funagata is made up of andesite, which is easily distinguished from the pigeonite basalt that erupted from Mout Kurohana. The crater that produced Mount Izumigatake is located on a ridge between Izumigatake and Kita-izumigatake (North Izumigatake).