Within the Marble Mountain-Trout Creek Hill field, there have been three eruptions during the Holocene epoch: at West Crater, another cone near Hackamore Creek, and a phreatic vent (producing steam and rock fragments) near Bare Mountain. These all took place about 8,000 years ago. The West Crater eruption generated an andesitic lava dome and lava flow, while the Bare Mountain vent formed a large explosion crater at Bare Mountain.