Valles Caldera
Found near Santa Fe, New Mexico, the Valles caldera is about 175 square miles in area. It exploded about 1.2 million and 1.6 million years ago, with ash and rock reaching as far as Iowa. Geologists suspect that the Valles caldera explosion is related to how the tectonic plates under the United States western portion is moving away from the rest of the North American tectonic plates.
