Are There Really Fish Fossils on This Mountain?

In the Beartooth Range of Montana, easy to reach on the beautiful Beartooth Highway (U.S. 212) from Yellowstone’s Northeast Entrance, stands Beartooth Butte. Partway down from its 10,514 foot (3,200 m) summit, within the dark red zone of rocks, geologists have found fish fossils as old as 400 million years. That’s a little hard to picture, but this is how they explain it.

Sedimentary rocks containing the fossils were laid down at the bottoms of streams and seas then covering the area. But some 50 million years ago, gigantic forces uplifted the entire area. The layers uplifted were both the sedimentary rocks and the much older rocks below them. Although the younger rocks have mostly been eroded away, enough remain on Beartooth Butte to leave evidence of that very different environment so long ago.

CREDITS: Text and photo by Bruno Giletti.

IN THE GUIDEBOOK: You’ll find a lovely photo of the butte on page 188 of Yellowstone Treasures, sixth edition. Another fascinating geologic enigma in the area just northeast of Yellowstone is described in “Heart Mountain Detachment,” pages 303–4, and shown on the map on page 300.

Copyright Bruno Giletti. All Rights Reserved. Updated January 23, 2021