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Copyright 2010 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor;


The World-Famous Hagerman Fossil Beds

Article by Natalie Riehl 


July 2010 Issue



This painting in the Visitor Center depicts what the Hagerman area may have looked like 3.5 million years ago. Photo by Rick Landry.


     Most horse lovers know that horses once existed in North America , died out, and were reintroduced by the Spanish explorers. But how many people know that horses originated and evolved in the area that is now Idaho and Oregon , and crossed over the Bering Land Bridge to Asia and the continent beyond?

     In May, we visited the Hagerman Fossil Beds National Monument to investigate their collection of equine fossils which look surprisingly “modern,” even though they are 3.5 million years old.

     The equine fossils were first discovered in 1928 by area rancher Elmer Cook. Initial excavations by the Smithsonian Institution began in 1929 and continued into the early 1930s. Paleontologists discovered a large concentration of fossils of an extinct species of horse, which became known as the “Hagerman Horse.” Eventually 120 horse skulls and 20 complete skeletons were excavated from the Horse Quarry.

     Later expeditions revealed that the area contained the highest concentration of Pliocene fossils found anywhere in the world. The Smithsonian has exchanged some of their horse skeletons with other museums around the world, and this has brought international recognition of the Hagerman Horse.


Replica of a complete Hagerman Horse fossil in Visitor Center . Rick Landry photo.


The “Hagerman Horse” is the earliest equine to bear the genus Equus — Equus simplicidens. It is believed to be more closely related to Grevy’s Zebra, which now lives in southern Africa , than to modern horses.

     It was about the same size as a modern-day zebra, standing about 43–57 inches high at the shoulder (10.3 – 14.1 hands), and weighing 385 – 847 pounds.

     Although the area today is high desert, during the Pliocene Epoch, it was a lush green floodplain flowing into ancient Lake Idaho . Grassy plains received more than 20 inches of precipitation annually; today’s annual rainfall is 10 inches.

     In addition to the horse skeletons, hundreds of fossil sites in the area have produced fossils from more than 180 animal species, both vertebrates and invertebrates, and 35 plant species.

     Animals which lived here at the time of the Hagerman Horse include mastodons, camels, saber-tooth tigers, beavers, muskrats, otters, antelope, deer, ground sloths, hyena-like dogs; fish, frogs, and snakes; and waterfowl such as pelicans, herons, and swans.

     The climate eventually changed and the animals had three options: adapt, migrate or become extinct. Animals which adapted include beaver and muskrat and numerous species of birds. Those which mi-
grated include llamas to South America, and horses and camels into Eurasia . Those which became extinct include ground sloths, mastodons and other large herbivores. As their prey disappeared, saber-tooth cats and hyena-like dogs also became extinct.

Genuine fossil of Hagerman Horse skull in Visitor Center . Photo by Rick Landry.


     A question that has stumped paleontologists: Why are there are so many horses in this one site?

     One hypothesis is perhaps the horses were swept away in a flood and quickly buried in the river channel. A problem exists in that the majority of skeletons are disarticulated or partially articulated, and this indicates that they were exposed on the surface.

     A second hypothesis is that, in a time of severe drought, these animals died while hanging around the watering hole in a dying river bed. When the rains came, the bones would be buried. However, the dying animals would attract predators, and of the over 200 individual horses recovered, none bear carnivore gnaw marks.

     The National Monument, established in 1988, is located in Hagerman , Idaho , on the Snake River, about 37 miles west of Twin Falls . The “monument” consists of a Visitors Center in town and a 4,300- acre tract of land on the west side of the river.

     The visitors’ center is a small, modest building which contains a replica of one of the complete equine fossils discovered at the horse quarry, plus a few displays which describe the geology of the area and the paleontological record. Also of interest, is a small room that houses Minidoka Japanese Internment camp memorabilia and photos.

     There is no access to any of the actual quarry sites, as they are scattered throughout the 600-foot high bluffs which rise from the Snake River . A drive to the Monument land will provide visitors with two overlooks; one not far above the river’s surface and a second on top of the bluff, which incorporates part of the historic Oregon Trail.

     Visitor Center hours vary, depending on the season. For more information about the Hagerman Fossil Beds, call 208-837-4793 or visit

     The author thanks the National Park Service for the numerous pamphlets and handouts distributed at the Hagerman Fossil Beds National Monument which were used as reference materials for this article.

Copyright 2010 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor;


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