The city of Mammoth Lakes sits on the edge of the Long Valley Caldera formed around 700,000 years ago. This caldera is 15 miles in diameter and is North America's second largest. 1. The Long ...

The Long Valley Caldera in northern California is waking up, and scientists are monitoring it. This supervolcano, whose last blast was some 100,000 years ago, isn’t leading up to another monstrous ...