Photograph of the skull of a Hagerman horse shows from the side. 

Fossils of the Columbia Plateau

Simple map showing the Columbia Plateau region of the northwest-central United States, which occurs entirely within Idaho.

Page snapshot: Introduction to the fossils of the Columbia region of the northwest-central United States.

Topics covered on this page: Proterozoic and paleozoic fossils; Mesozoic fossils; Cenozoic fossils; Hagerman Fossil Beds; Quaternary fossils; Resources.

Credits: Most of the text on this page comes from "Fossils of the Northwest Central US" by Warren D. Allmon and Dana S. Friend, chapter 3 in the The Teacher-Friendly Guide to the Earth Science of the Northwest Central US, edited by Mark D. Lucas, Robert M. Ross, and Andrielle N. Swaby (published in 2015 by the Paleontological Research Institution; currently out of print). The book was adapted for the web by Elizabeth J. Hermsen and Jonathan R. Hendricks in 2022. Changes include formatting and revisions to the text and images. Credits for individual images are given in figure captions.

Updates: Page last updated August 30, 2022.

Image above: Skull of a Hagerman horse (Equus simplicidens), Pliocene Glenns Ferry Formation, Idaho. Photo of USNM V 11986 by Michael Brett-Surman (Smithsonian National Museum of Natural History, public domain).

Proterozoic and Paleozoic fossils

Rock formations from the late Proterozoic are the oldest fossil-bearing formations in the Columbia Plateau region. The earliest fossils found here are stromatolites, similar to those seen in Montana’s Glacier National Park, which have been reported in the Gospel Peak area of northwestern Idaho.

Paleozoic rocks are not present in the Columbia Plateau, as the land has been covered with igneous rock related to eruptions of the Yellowstone hot spot as it moved along the track of the Snake River Plain.

Mesozoic fossils

Triassic rocks occur along the state’s border with Oregon and southern Washington. Here, deposits of metamorphosed volcanic and sedimentary rocks contain a variety of marine fossils. These include corals, sponges, ammonoids, clams, gastropods, echinoids, and bryozoans. The Columbia Plateau has Triassic red beds and thin deposits of coal, both of which indicate some terrestrial deposition.

Outcrops of Jurassic-aged rocks occur in western Idaho, along the border with Oregon and southern Washington. These rocks, formed mostly in deep water marine environments, have been slightly metamorphosed. Fossils from these rocks include ammonoids and oysters. Jurassic rocks in the southeastern part of the state are mostly shallow marine yielding mostly poorly preserved fossils, including crinoids, oysters, sea urchin spines, ammonoids, and corals.

Cenozoic fossils

Hagerman Fossil Beds

The Neogene river and lake sediments of westernmost central and southern Idaho contain abundant and beautifully preserved fossils of fish, rhinos, rodents, rabbits, horses, camels, and many other species. The Hagerman Fossil Beds National Monument on the Snake River just northwest of Twin Falls, south-central Idaho, is the most famous of these deposits, and includes Horse Quarry. This particular outcrop has yielded hundreds of fossils of zebra-like Hagerman horses (Equus simplicidens) that are about 3.5 million years old.

Photograph of a mounted skeleton of a Hagerman horse from the Pliocene of Idaho on display in a museum. The photo shows a complete horse skeleton mounted standing on four long legs, each ending in a hoof with one toe. The tail is short, the neck elongated, and the skull robust with a large lower jaw.

Hagerman horse (Equus simplcidens), Pliocene, Hagerman, Idaho. Specimen on display at the Royal Ontario Museum, Ontario, Canada. Photo by Daderot (Wikimedia Commons, CC0 1.0 Universal/public domain dedication).

Photograph of the skull of a dwarf pronghorn antelope from the Pliocene Hagerman Lake Beds, Idaho. The photo shows a skull missing the lower jaw, with the nose facing right. The skull has a large eye socket with a short, bifurcated horn above it. Total skull length is just over 15 centimeters.

Upper part of the skull of a dwarf pronghorn antelope (Ceratomeryx prenticei), Pliocene, Hagerman Lake Beds, Idaho. Photo by Michael Brett-Surman (National Museum of Natural History, Smithsonian Institution, pubic domain).

Photograph of the lower jaw of a giant marmot from the Pliocene Hagerman Fossil Beds of Idaho. The photos shows a partially preserved lower jaw with two chisel-like front teeth and a series of molars on each side. The bone is medium brown in color, the teeth dark brown to black. A white specimen box can be seen in the background.

Lower jaw of a giant marmot (Paenemarmota barbouri), Pliocene, Hagerman Fossil Beds, Idaho. Photo by S. Lacy, Nation Park Service (public domain).

Photograph of bones of a peccary from the Pliocene Glenns Ferry Formation of Idaho. The photo shows a skull at lower left with open mouth and a jumble of other bones scattered around it. All are exposed on a brown rock slab. The bones are off-white to light brown in color.

A fossil peccary (Platygonus pearcei), Pliocene, Glenns Ferry Formation, Idaho. Photo by Michael Brett-Surman (National Museum of Natural History, Smithsonian Institution, pubic domain).

Photograph of the lower jaw of a bone-brushing dog from the Pliocene Hagerman Fossil Beds of Idaho. The photo shows one half of a lower jaw with a long, pointed canine tooth and two molars. The jaw is held by someone wearing blue gloves with two hands. The jaw is light brown in color.

Lower jaw of a bone-crushing dog (Borophagus hilli), Pliocene, Hagerman Fossil Beds, Idaho. Photo by F. Brown, National Park Service (public domain).

Quaternary fossils

Remains of large Pleistocene mammals, like Columbian mammoths, mastodons, and bison, have been found in the Columbia Plateau. Examples include a group of mammoths at Tolo Lake in western Idaho (where a group of mammoths were found) and American Falls Reservoir in southeastern Idaho (where part of a mammoth was discovered and excavated in 2014).

Photograph of the lower jaw of an Edward's wolf from the Pleistocene Bruneau Formation of Idaho. The photo shows one side of a jaw, the with hinge toward the left and the tip (which has been broken off) to the right. A few molars are in the jaw. Total length is about 10 centimeters based on the scale at the bottom of the photo.

Lower jaw of an Edward's wolf (Canis edwardii), Pleistocene, Bruneau Formation, Owyhee County, Idaho. Photo by Michael Brett-Surman (National Museum of Natural History, Smithsonian Institution, pubic domain).

Photograph of teeth and jaw fragments from a fossil camel, Quaternary, Oregon. The photo shows seven isolated teeth and two jaw fragments with teeth laying on a black velvet background. There is no scale bar.

Camel teeth and jaw fragments (Camelops minidokae), Quaternary, Idaho. Photo by Michael Brett-Surman (National Museum of Natural History, Smithsonian Institution, pubic domain).

Photograph of the excavation of mammoth bones at American Falls Reservoir, Idaho, in 2014. The photo shows four men excavating a large mammoth bone stuck in a bank and partially exposed. One of the men standings in water next to the bank, looking at another man who is crouched by the bone and excavating it. Another man in the background also appears to be working on the bone, whereas a fourth men standing on the bank is taking notes. Two other people can be partially seen on the slope above the bank.

Excavation of Columbian mammoth remains at American Falls Reservoir, Idaho, in October of 2014. Photo source: Bureau of Reclamation on flickr (Creative Commons Attribution-ShareAlike 2.0 Generic license, image resized).

Resources

Resources from the Paleontological Research Institution & partners

Digital Atlas of Ancient Life Virtual Collection: https://www.digitalatlasofancientlife.org/vc/ (Virtual fossil collection featuring 3D models of fossil specimens sorted by group)

Digital Encyclopedia of Ancient Life: https://www.digitalatlasofancientlife.org/learn/

Earth@Home: Earth Science of the Western United States: Fossils of the Columbia Plateau (continues coverage of the Columbia Plateau in northern Nevada, Oregon, and Washington): https://earthathome.org/hoe/w/fossils-cp

Earth@Home: Quick guide to common fossils: https://earthathome.org/quick-faqs/quick-guide-common-fossils/

Go to the full list of resources about fossils in the northwest-central U.S.
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