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Glacier activity, volcanoes, and erosion have all affected the Tower-Roosevelt Area’s landscape. Mountains were thrust to the sky, and ancient forests were preserved in ash. Today, the geology of the area continues to change and provide new keys to Yellowstone’s violent past.

Volcanic Activity
Eruptions pounded Yellowstone forty-five to fifty million years ago, and as a result, mountains in the Tower-Roosevelt Area began to form. Further volcanic activity strengthened the bases of these mountains and forced the peaks to reach even higher, creating the region’s tallest peaks at Mt. Washburn and in the nearby Absaroka Mountain Range. At the same time, tons of volcanic ash rolled across the region’s forests, blanketing them in debris and preserving their cellular structure to this day in petrified remains.  

Glacial Events
Following Yellowstone’s last major volcanic eruption, glaciers barged across the region, moving mountains of ash and unearthing the petrified trees of a once colorful and vibrant forest. In their wake, glaciers left behind boulders, moraines, and lakes. Two of these ancient lakes once filled the Hayden and Pelican Valleys. The remaining lakebeds are now thriving meadows supporting a range of wildlife. Glacial moraines are also evident to this day in the Lamar Valley, the Hellroaring and Slough Creek drainages, and on Blacktail Plateau.

Forces of Erosion
For millions of years, running water has served as the Tower-Roosevelt Area’s primary erosion force. Gravity and water combined to create the area’s astounding features, including Tower Fall and its surrounding rock pinnacles, the Black Canyon, and the highly reputed Grand Canyon of the Yellowstone.

Water has also helped expose large outcrops of schist and gneiss in the Tower-Roosevelt region. Dated more than two billion years old, the rocks are among Yellowstone’s oldest features. Although it may appear Yellowstone has reached the pinnacle of its natural beauty, erosion is still at work. The mighty power of running water continues to mold and craft new and existing Yellowstone features under visitors’ watchful eyes.

Geological Overview of the Tower-Roosevelt Area