La Garita Caldera is a large supervolcanic caldera in the San Juan Mountains. It is near the town of Creede in southwestern Colorado, United States.
The volcanic eruption is one of the largest known in Earth's history and one of the most powerful known supervolcanic events. This eruption had a Volcanic Explosivity Index (VEI) of 8, the highest on the scale.
All mountains and calderas on the West coast of the Americas have the same root cause: they are all a product of the western move of the Americas, which has been going on for millions of years. That is basically why the Americas have mountains in the West, and lowlands in the East.