Valles Caldera (New Mexico)
Rolling meadows and dense forests mask this 13-mile-wide depression formed 1.25 million years ago. Hot springs and gas vents dot the landscape, signaling heat below. Elk graze peacefully in the vast crater, creating postcard-perfect scenes. Its last significant eruption occurred 50,000 years ago. The caldera now serves as a national preserve where visitors often fail to recognize its volcanic origin.