Mountain Press  Roadside Geology of Yellowstone Country - 2nd Edition

From the publisher: With more than 10,000 geysers, hot springs, fumaroles and mud pots, as well as cubic mile upon cubic mile of once-incendiary rhyolite, the landscape of Yellowstone Country vividly displays its fiery past and present. The region contains 1/5 of the world's geysers, including the most famous of them all, and is the setting of some of Earth's most destructive volcanic eruptions.

The road guides deliver you to such sites as exquisitely preserved, 50-million-year-old petrified trees buried in conglomerate; mountain-sized blocks of rock that slid more than 50 miles in a massive debris avalanche; the glacially carved craggy peaks and U-shaped valleys of the Beartooth Mountains and Absaroka Range; and the Grand Canyon of the Yellowstone, the excavation of which is still a mystery.