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Idaho SuperGraphic

The evolution of Idaho's ancient savannah

Ancient bluffs, 600 feet above Idaho's winding Snake River and six miles long, comprising the Hagerman Fossil Beds reveal many clues about the landscape during the end of the Pliocene Epoch. Sediment layers from river level to bluff tops span 550,000 years... from 3.7 million years old at river level to 3.15 million years old at the top of the bluff. The bluff layers were deposited from the carving action of the rivers that flowed into ancient Lake Idaho, that came and went through time, flooding the countryside. Fifteen thousand years ago, the Bonneville Flood carved the high bluffs, gouged out canyons, moved house-size boulders and left enormous sandbars throughout the Snake River Canyon while exposing the layers and fossils.


More than 3 million years ago along the shores of the now- extinct Lake Idaho, strange horse-like creatures galloped across the land. The ice age had not yet begun and the land was savannah-like with green grasses, isolated patches of pine woodland and abundant hardwood trees, receiving double the rainfall that southern Idaho gets today. The area was once a floodplain, and the sagebrush landscape of present day Idaho is very different than the environment at the time the Hagerman Horse roamed. The Hagerman Horse shared the ancient grassy plains and ponds with mastodons, saber-toothed cats, beavers, muskrats, otters, camels, antelope, deer, ground sloths, hyena-like dogs, fish, frogs, snakes and waterfowl. Most of the animals and other life forms that were alive during the Pliocene would have been strange looking, yet recognizable by us today. Many individual species were different, but research shows that distinguishing characteristics of various animal and plant groups were present. The Hagerman Horse, the early zebra-like version of a modern-day horse, was well adapted to life on the grassy savannah. So what happened? Why did the Hagerman horse disappear?

Related images

camel skeleton
A camel living during the Pliocene Epoch, sharing the grassy plains with the Hagerman Horse.
Courtesy of the National Park Service.
Drawing of a ground sloth skeleton
A ground-sloth living during the Pliocene Epoch, sharing the grassy plains with the Hagerman Horse.
Courtesy of the National Park Service.

A horse is a horse... Unless of course The disappearing act