A petrified redwood reveals a warmer, damper, more violent Yellowstone landscape. The trunk is anatomically indistinguishable from present-day redwoods in California. In Eocene times 50 million years ago, a chain of volcanoes erupted here and triggered massive landslides into mountain and valley streams. A rolling mix of ash, water, and sand buried forests, and before the trees could rot, abundant silica in the volcanic flow plugged living cells, creating forests of stone.