Scientists think West Crater erupted during the Holocene epoch, about 8,000 years Before Present. Its lava flows intermix with tephra from an eruption of Mount St. Helens and tephra from the climactic eruption of Mount Mazama about 7,700 years ago. Within the Marble Mountain-Trout Creek Hill field, only two other volcanoes have erupted during the Holocene: the volcanic cone near Hackamore Creek and a phreatic crater at Bare Mountain's summit. These cones were likely active simultaneously, as one of the lava flows from West Crater is embedded with an andesitic lava flow from the Hackamore Creek cone. Their similar ages and locations imply that they resulted from the same movement of magma and were possibly fed by the same magma chambers.