During the past 35,000 years, volcanic activity in the the Long Valley area has been confined to the Mono-Inyo Craters volcanic chain. About 20 small to moderate eruptions have occurred somewhere along the chain in the last 5,000 years, as shown in diagram above. Some of the eruptions occurred at about the same time and in close proximity. For example, the Inyo eruptions 550 to 600 years and the eruptions from the north end of the Mono Craters about 600 years ago. The intervals between eruptions or eruption clusters ranges from 250 years to 750 years.