As you leave volcanic Yellowstone, and travel eastward through Silver Gate and Cook City, Montana you have to the north the Beartooth Mountains of basalt and schist. These were thrust up some 85 million years ago and reveal some of earth’s oldest rock. They also pushed up some 6 to 10 thousand feet of sedimentary rock that is almost completely eroded. There are only a few outcropping of that rock remaining atop the grey and black rock like icing on a cake. Beartooth Butte (below) is one that remains. Otherwise you see only the basalt and schist that forms a rolling plateau along the entire Beartooth mountains. In the early summer this plateau is a green carpet filled with miniature renditions of the flowers that grow at lower elevations. This carpet seems to go on for miles. In late summer the land turns brown as if a rug was removed showing the mat pad underneath.
To the south of US 212 is valley containing the Clarks Fork of Yellowstone river and the volcanic built and glacial sculpted Absaroka Mountains. If you look at the picture above, you will see that these grey mountains sit on top of a line of white sedimentary rock following the river. That line of sedimentary rock slopes to the east at about 2 degrees and ends some 50-miles away at the lump of sedimentary rock that is the “Heart Mountain detachment”. How that rock got here is a great story of nature at her best manipulating mysteries.
The crest of Heart Mountain, which is just to the north of Cody,Wyoming is part of a geological event that has puzzled scientists for years. The Heart Mountain formation is the end result of a line of rock some 6,000 feet thick that slid laterally 40-miles down the valley and over a mountain range to land where it sits today. There is no where else in the world where will you see that! Now consider this additional fact, the entire rock formation above the white line that follows the valley, was some thirty miles long and several thousand feet thick when it slipped away. Geologists believe that the slide event did not last over 4 minutes.
In the picture above look for the white line below the grey-black volcanic rock. everything above it slid to the left and the Yellowstone’s volcano filled in on top.
A recently released book on the geology of this area discusses all of this phenomena in layman’s terms. The book is “east of Yellowstone” – not relation to this site other then it is about the same area. “East of Yellowstone” is must reading for any curious traveler in the triangular area north of Cody, Wy., west of Red Lodge, Mt. and east of Yellowstone. ISBN 978-1-879628-38-0
You can purchase it by phone for $25 from the publisher Keokee Co. Publishing, Inc. Call 1-800-880-3573 ”east of Yellowstone”