Eruptions of basalt and andesite 400,000 to 60,000 years ago in the west moat of Long Valley Caldera were the first activity associated with the Mono-Inyo Craters system. Eruptions around 300,000 years ago filled the west moat with of basaltic lava.: Basaltic and andesitic eruptive activity then moved to Mono Basin and lasted from 40,000 to 13,000 years ago.