La Garita Caldera (USA)
Colorado’s San Juan Mountains hide remnants of one of Earth’s largest known eruptions. The cataclysm 27 million years ago ejected an astonishing 1,200 cubic miles of ash. Dramatic cliff formations and sweeping vistas reveal its ancient outline. Though dormant for millennia, its scale humbles researchers. Hikers traverse its weathered rim, often unaware they’re walking on a prehistoric supervolcano.