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The Mono Craters are the youngest mountain range in North America. Rising up to 2400 feet above the surrounding Mono Basin, the Mono Craters first began erupting as early as 100,000 years ago. Eruptions were well under way by 40,000 years ago and most of what we see today as the Mono Craters was formed within the last 10,000 years. Much of the visible surface of the Mono Craters is composed of pumice and obsidian. Local Indians would later use obsidian to fashion arrowheads and cutting tools. Careful measurement has shown that this fracture or fault, has been inactive for the past 40,000 years, about the time when the Mono Craters became active. The Mono Craters are not dead. They remain dormant and will almost certainly erupt again in the future. When the L.A. DWP drilled an 11.5 mile aqueduct tunnel through the Mono Craters in the 1930ís, work crews encountered hot and cold groundwater, deadly carbon dioxide gas, and steam proving that there is still activity within the Mono Craters. Nobody knows when the next eruption will be, but geologic changes occur extremely slowly when compared to the human lifetime.
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