Scientists Found 200+ Species of Prehistoric Animals Perfectly Preserved in This Idaho Valley

Hagerman Fossil Beds, Idaho

Three million years ago, southern Idaho was home to zebras, camels, and saber-toothed cats. Today, their bones tell stories buried in ancient lake beds along the Snake River.

Here’s what makes this fossil graveyard so remarkable.

A Rancher Notices Bones in the Bluffs

Elmer Cook spotted unusual bones eroding from the steep bluffs above the Snake River in 1928. The local rancher immediately contacted Harold Stearns of the U.S. Geological Survey.

Stearns recognized their importance and notified the Smithsonian Institution in Washington, D.C. His quick action brought paleontologists to Idaho the following year.

Cook didn’t just report his discovery.

He worked alongside Smithsonian crews for seven excavation seasons until his death in 1961, while his wife Lydia sometimes prepared meals for the fossil hunters.

Smithsonian Teams Unearth Prehistoric Treasures

Smithsonian teams excavated at Hagerman from 1929 to 1934.

Dr. James Gidley led the first expeditions, removing hundreds of cubic yards of sediment to reach bone beds 45 to 60 feet below the surface.

When Gidley fell ill in 1931, Norman Boss took over. That year alone, workers uncovered five complete horse skeletons, 32 skulls, and 48 lower jaws.

In 1934, new curator Dr. C.L. Gazin continued the work, uncovering 65 more horse skulls.

By the end of the Smithsonian expeditions, fossils of over 200 individual horses filled the museum’s collections.

North America’s First True Horse Takes Shape

The Hagerman Horse galloped across the Snake River Plain 3.5 million years ago.

Scientists identified it as Equus simplicidens, the earliest known member of the modern horse genus.

Standing at the shoulder height of an Arabian horse, this animal more closely resembled zebras than modern horses based on its skeletal structure.

Idaho designated this prehistoric horse as its official state fossil.

The Hagerman Horse represents a pivotal moment in equine evolution, establishing the single-toed foot characteristic of modern horses.

When Idaho Resembled Modern Africa

Three million years ago, the Hagerman area looked nothing like today’s arid landscape.

Lush wetlands surrounded broad rivers that flowed into ancient Lake Idaho. Forests grew alongside grassland savannas similar to those in modern East Africa.

Volcanic ash from distant eruptions occasionally blanketed the land.

The sediments from this time comprise the Glenns Ferry Formation, which reaches 600 feet thick in places.

These layers preserved the diverse ecosystem of the Pliocene epoch, capturing plants and animals through successive layers of mud, sand, and ash.

Death Trap at the Drying Waterhole

A severe drought struck the Snake River Plain 3.5 million years ago.

As water sources disappeared, desperate animals congregated at a shrinking pond or marsh in what would become the Hagerman Horse Quarry.

Dozens of horses, along with other animals, died from thirst, starvation, and disease around this dwindling water source. Their bodies decomposed where they fell.

Later, a flash flood swept through the dry basin, moving the bones a short distance before burying them in sediment, creating one of paleontology’s richest bone beds.

Strange Mammals Roam the Hagerman Valley

Mastodons browsed in the cool forests of Pliocene Idaho, and camelops, North America’s native camel, traveled these grasslands before its kind disappeared from the continent.

Ground sloths moved slowly through the landscape on massive clawed feet, among many other mammals that are now extinct.

Life Along the Ancient Rivers

The beaver Castor californicus built dams and lodges in Hagerman waterways 3.5 million years ago.

Its fossils show striking similarities to modern beavers, with the same chisel-like teeth and flat, scaly tail structure. Two otter species shared the waters.

The cat-sized Lontra weiri, discovered in the 1980s but only correctly identified in 2014, represents the oldest known New World river otter.

Its larger relative, Satherium piscinarium, grew to the size of a Labrador retriever. These water-dwelling mammals hunted fish preserved as fossils in the same sediments.

Pioneer Wagons Cross the Fossil Record

Oregon Trail emigrants trudged through the Hagerman area beginning in the 1840s, unaware they walked above a paleontological treasure.

The southern route of the famous trail cuts directly through what is now the Monument.

The area’s sedimentary geology provided one of the few access points to reach the Snake River, vital for emigrants and their livestock after crossing arid lands.

Heavy wagons carved deep ruts into the soft soils, permanent tracks still visible today. The Oregon Trail Overlook offers views of these historic wagon tracks from 180 years ago.

From Discovery to National Protection

The National Park Service and Smithsonian recognized Hagerman’s importance, designating the Horse Quarry as a National Natural Landmark in 1975.

Congress elevated the site to National Monument status in 1988.

In 2014, Hagerman formed an international partnership with Kenya’s Sibiloi National Park, connecting two world-class fossil sites on different continents.

The Hagerman Paleontology, Environments, and Tephrochronology Project launched in 2016, combining National Park Service and U.S. Geological Survey researchers to better understand the ancient landscapes through volcanic ash dating.

Visiting Hagerman Fossil Beds National Monument

The Thousand Springs Visitor Center opened in April 2022 at 17970 Highway 30, one mile north of downtown Hagerman.

This facility serves both the Monument and Idaho’s Thousand Springs State Park through an innovative partnership.

Two overlooks along Bell Rapids Road provide views of the Snake River and Oregon Trail. A 3-mile hiking trail connects these overlooks, following the historic emigrant route.

The visitor center displays fossil exhibits, offers ranger programs, and provides maps for exploring both parks. No excavation sites are open to the public.

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