GRANITE PEAK PUBLICATIONS: Books accompanying travelers to the Park since 2002

How Did These Mountains Get Striped?

Abiathar Peak

Abiathar Peak

On both sides of the Northeast Entrance Road in Yellowstone, you can see mountains that look like a slice of layer cake. One example is Abiathar Peak (pronounced uh-BI-uh-ther) of the Absaroka Range. They are geological evidence of some of the processes that have shaped the area over the past 350 million years. In that long-ago era, a quiet sea covered everything here. Remains of tiny marine organisms accumulated at the bottom of undisturbed water. In time, and as additional sediments pressed down from above, these remains became cemented together to form limestones.

Pyramid Mountain

Pyramid Mountain

More recently, around 50 million years ago, volcanoes erupted repeatedly near here, sending layers of lava across the landscape and covering the older rocks. (See how this fits into the Geological Time Line.) What we see today are some of the flows but also a lot of debris from giant mud slides that carried down the volcanic sands, gravels, and boulders together to create these mixtures, called conglomerates. Now, as we look at these mountains of the Absaroka Range, erosion has exposed the edges of the various colored layers.

CREDITS: The text and both photos on this page are by Bruno Giletti.

IN THE GUIDEBOOK: Learn much more about the park’s varied geological history in “The Stories in Yellowstone’s Rocks,” written by geologists Bruno Giletti and Jo-Ann Sherwin, pages 302–318 in the fourth edition of Yellowstone Treasures.

Copyright Janet Chapple. All Rights Reserved.

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