summer 2001 : features

Hagerman Fossil Beds

A Window to Idaho's Past

by Greg Stahl

A sabertooth tiger saunters amidst dense hardwood trees near the southwest corner of what is now the state of Idaho. Giant marmots, camels and deer part before the ancient predator like the Red Sea before Moses.

The grasses are green, and the prairie is savanna-like. It’s a wetter place than now. 

The large cat, with long canines protruding from its jaws, approaches the bank of a river, flowing smoothly to the south and west. The mouth of the river, just downstream from the primitive predator, empties into Lake Idaho, a massive body of water covering parts of what are now Idaho, Nevada and Oregon.

On the adjacent river bank, ancient horses dip their heads in the river’s refreshing waters, and, perhaps, one gets stuck in the muddy riverbank. It bucks and throws for a while, before resigning itself to the inevitable. 

The herd moves on, leaving the lone horse to die in the muddy, meandering river. As weeks turn to months, the horse’s bones settle in the mud and sand near the riverbank. Subsequent runoff covers the bones beneath layers of sediments. The river changes course. Lake Idaho ebbs and flows, depositing still more layers of dirt and sand over the once-living bones.

Centuries pass, and the bones are preserved in the belly of the earth, but under a hot desert sun in 1929, scientists dig them out, dust them off and attempt to put the pieces of this complex series of events back together.
Mother Earth’s mysteries.

The Snake River weaves through Idaho’s 2,000-foot-high Snake River Plain, draining southern and central Idaho, western Wyoming and forming a great valley at the city of Hagerman that reveals 4 million years of fossilized and geologic history.

In the southwest corner of Idaho, on the southwest corner of the Snake River Plain, lies the Hagerman Fossil Beds National Monument, which includes one of the richest fossil deposits—particularly of ancient horses—ever discovered in the United States. It also includes a portion of the Oregon Trail, which East Coast emigrants traveled on a pilgrimage to a new way of life in the West in the early and mid-1800s.

Fossil and geologic records indicate it wasn’t always this way. The area once consisted of thriving riparian and grasslands ecosystems, receiving double the precipitation that southern Idaho gets today. It was “diverse and varied,” says fossil beds education specialist Judy Hart, and was home to sabertooth cats, camels, giant marmots, sloths, snakes, bears and the most famous Hagerman discovery, the Hagerman horse.

On a national park scale—or even on the scale of a national monument—the fossil beds is a small park. Each year about 13,000 visitors search out the ancient secrets hidden in the towering sedimentary walls above the Snake River. The 4,000-acre park borders six and a half miles of Snake River waterfront on the south side of the river.

The national monument protects the world’s richest known fossil deposits from the late Pliocene time period—1.8 million to 5 million years ago. The diverse Hagerman fossil specimens represent the last vestiges of species that existed before the Ice Age and the earliest appearances of modern plants and animals. 

The deposits are contained in continuous, uninterrupted geologic strata exposing 500,000 years of an intact Pliocene-era ecosystem, including wetland, riparian and savanna habitats.

More than 550 fossil sites are documented at different horizons within the sediments. The best known discovery, the Hagerman horse, Equus simplicidens, is the official Idaho state fossil. The Hagerman Horse Quarry, a national landmark, “is recognized as one of the most important sites in the world related to the fossil history of the horse,” states the National Park Service in its management plan for the area.

“This is probably the most important site in the world for this species,” says Bill Hart, Judy’s husband and a geologist at Miami University in Ohio. “And the horse has played a major role in the development of the West.”

What makes the discovery of Hagerman horse fossils in Idaho so important is the sheer number of the samples taken from the Hagerman Horse Quarry, which was first excavated by the Smithsonian Institution in the early 1900s. More than 200 animals of both sexes and all ages were recovered. Included in the find are complete skeletons as well as skulls, jaws and detached bones. No one knows why so many animals died in the same place at approximately the same time, and theories are varied.

Despite the popular use of the name, Hagerman horse, the animal is actually more closely related to the zebra, specifically the Grevy’s zebra of Africa. Judy says it’s commonly accepted that the Hagerman horse, “the closest ancestor to the modern horse,” went extinct in North America 10,000 years ago, but some of the animals may have previously migrated from North America to Asia.

It was 8,500 years later that Europeans brought the Hagerman horse’s progeny—modern horses—back to North America.

“If these animals can’t adapt and don’t migrate, they go extinct as the environment changes,” Judy says. “When you think of all the life that’s been on earth and only a fraction of it is preserved as fossils, there’s just so much that we don’t know.”

The plight of the Hagerman horse is among those mysteries.

Also preserved at the monument are more than 200 species of vertebrates, invertebrates and plants. The monument’s high concentration of fossil sites from a relatively short geologic span of time makes possible the understanding of geologic events, environmental changes and biodiversity not possible for most fossil areas.

“There’s a saying in geology that says the present is the key to the past,” Bill says, “and, to some degree, the past is the key to the present as well. You can learn about what is by understanding what was. This place had a lot more rainfall, a lot more vegetation, and we know that from the fossil and geologic records.”

 

Formation of the Hagerman Valley

Three and a half million years ago, the area now called Hagerman was a floodplain on the northeastern margin of a large lake, now popularly called Lake Idaho. 

Equaling any one of the modern Great Lakes in size, Lake Idaho received the sediments transported by the ancestral Snake River and other streams cutting across what is now the Snake River Plain. Perhaps, it is theorized, the lake even covered the area now known as Hagerman at different times during its existence.

Unlike the sagebrush steppe environment of today, the Snake River Plain of the late Pliocene was savanna-like, with patches of woodland. Water was more abundant, and hardwood trees like willows, elms and birches grew beside rivers and streams.

“Based on the types of plant pollen found, rainfall is estimated to have been 20 inches a year, about twice the amount that falls on the region today,” reports Gregory McDonald, a paleontologist who worked at the monument until last fall. “That the overall environment was wetter is indicated by the vertebrate species found at Hagerman,” he writes in a report called “More Than Just Horses,” which was printed in Rocks and Minerals magazine in 1993.

Many of the fossilized birds found at Hagerman are associated with aquatic habitats. They include pelicans, herons, egrets, storks, swans, ducks and geese. Frogs and turtles are also abundant in many fossil sites, as are fish.

In addition, aquatic mammals are commonly found in the Hagerman strata and include ancestral muskrats, extinct beavers and otters. The fauna was not entirely aquatic, however, and many of the species—such as the Hagerman horse, camel and antelope—indicate that grassland was also plentiful. It was probably the seasonal flooding of streams and the ebb and flow of Lake Idaho that provided the sediments that quickly buried these animals’ skeletons and bones, resulting in the wealth of fossils preserved at the monument today.

The fossils were preserved deep within the sedimentary deposits. Long after Lake Idaho dried up, another geologic event created the Hagerman Valley as it is today, revealing the fossils preserved there.

Hagerman Valley formed 15,000 years ago when the Bonneville flood gouged out canyons, moved house-sized boulders and left enormous sand bars throughout the Snake River Canyon. 

The flood occurred when Lake Bonneville, a significantly larger version of the Great Salt Lake in Utah, overflowed into Idaho over what is now called Red Rock Pass near Pocatello. The flood, which occurred over the period of a few months and drained about 600 cubic miles of water from Lake Bonneville, filled the Snake River Canyon, creating a catastrophic torrent that overflowed the canyon’s rims. The most spectacular Bonneville flood deposits are giant gravel bars over 100 feet high.

Hagerman Valley’s landscape is dotted with incalculable numbers of rock “melons”—smooth and rounded off rocks—that remain as modern-day remnants of the colossal flood of yesteryear.

The flood also cut away the soft soils on the Snake’s southern border at Hagerman, revealing the 600-foot wall of well-defined sediments that’s there today.

 

More than fossils

“We are fossils, yes, but we are so much more,” says Judy, who laments the park’s relatively low visitor count and has a vision for better community interaction and better recreational opportunities at the park.

The park has several scenic trails that weave along the Oregon Trail, climb the 600-foot wall of sediments, pass through majestic cottonwood trees or skirt the canyon rim. The trails are generally short—totaling about 10 miles in all—and vary from easy riverside saunters to rigorous climbs to the canyon rim.

The park’s Emigrant Trail parallels the Oregon Trail for three miles, climbing about 500 feet of the park’s sedimentary deposits. Wheel ruts from long-passed wagon trains are still visible in the soft dirt of the valley’s southern shore.

“Our mission is to educate the public and let them know why this is such an important area,” Judy says. “We find scattered bones, and it’s our job to put them back into some kind of order. Until you really know what you’re looking at, you have no story. You just have bones.”

 

Valley of the Thousand Springs

(click on maps for larger versions)

The Hagerman Valley, known as “The Valley of the Thousand Springs” for its abundance of hot and cold water springs, is a rare, natural rest stop that’s served travelers for thousands of years.

Native Americans once stopped in the valley each spring and fall to fish salmon runs in the Snake River, which weaves through the gut of the valley. Some tribes wintered there because of the valley’s mild weather.

Today, the area is an attraction for fishing, white water rafting and kayaking, water skiing, bird watching and hiking.

The city of Hagerman, which gives the valley its name, was originally the site of a stagecoach stop along the Oregon Trail. The town was established in 1892 when Stanley Hageman and Jack Hess opened a post office and general store near what is now the town’s center. The city was named for Hageman, but a misspelling in the central post office registry changed the name to Hagerman.

Today, the valley is the largest producer of commercial trout in the world. The mild climate and abundance of year-round open water also make the valley a preferred stop-off for migrating waterfowl.

In addition to the Hagerman Fossil Beds National Monument, the valley is home to Malad Gorge State Park. The Malad River crashes down stair-step falls and into a pool called Devil’s Washbowl, then cuts through a beautiful 250-foot gorge on its way to the Snake River.

Views of the gorge are best from the sturdy, 175-foot-high bridge that crosses the canyon, from the rim, just off of Interstate Highway 84.

For more information on this unique area, check out the website: www.hagerman-idchamber.org