La Garita Caldera

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 eruption which made the caldera is one of the largest known volcanic eruptions in Earth's history. and one of the most powerful known supervolcanic events.
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.