Underneath Yellowstone sits one of the largest volcanic systems on Earth — a magma chamber the size of a small state. This is the longest history episode in the series, and it earns the length: the world's first national park is also a supervolcano, an 11,000-year homeland, and the stage for one of the most dramatic ecological recoveries ever documented.

Host Shawn Spainhour, a former Army officer, builds the whole story from the ground up — starting underground, with the hotspot that's been burning for 17 million years, the three catastrophic eruptions that shaped the continent, and the geyser-and-hot-spring system still running today. Then the people: the Tukudeka who lived the high country year-round, the obsidian trade that reached Ohio, the Nez Perce fighting retreat across the plateau in 1877, and the uncomfortable truth that "pristin ...