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11. Rattlesnake Tuff: Oregon’s largest known eruption

Exotic Terranes

Seven million years ago, from a volcano beneath the modern Harney Basin, a single gigantic eruption launched a huge cloud of red-hot ash, gas, and broken rock tens of thousands of feet into the atmosphere. The debris fell back to Earth and blanketed one fifth of the state (18,000 square miles) in a red-hot layer that welded itself into a compact volcanic rock and completely transformed the landscape of Oregon in just a few hours or days. Geologists call this rock the Rattlesnake Ash-Flow Tuff. Although this eruption was one of the largest, it was only one of hundreds of rift volcanosee Unit 9 eruptions left in the wake of the Yellowstone hot spot.

OGDC units: includes the Miocene Rattlesnake Tuff and Rattlesnake Formation

Age Range: 7 million years ago
Rock Types: tuff
Did You Know? Ash-flow tuff from the Rattlesnake eruption has been found up to 100 miles away from the vent.


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