Explore Geology
geology fieldnotes title

Agate Fossil Beds

National Monument


cover of park brochure

park geology subheading
Photo of fossil hills at Agate Fossil Beds
Agate Fossil Beds National Monument, Nebraska

Nineteen million years ago strange creatures walked a Miocene savanna. Careful digging at these quarries has brought to light the bones of these animals so long extinct.

About 19-20 million years ago a drought occurred in the plains of western Nebraska. Deprived of food, hundreds of animals died around a few shallow waterholes. Over time the skeletons were buried under silt, fine sand, and volcanic ash, carried by the wind and reworked by streams. A large fossilized waterhole with hundreds of skeletons is preserved today in the Niobrara River valley at Agate Fossil Beds National Monument. The discovery of this deposit and others nearby in the early 1900's was important to the developing science of paleontology. The study of these fossils-then and continuing today-have helped answer questions about the past. But what were the conditions that created this drought and brought these animals together?

Millions of years before the drought took place, sediments from eroding mountain ranges to the west were laid down to form the bed of a shallow sea during the "Age of Dinosaurs". About the time of the extinction of dinosaurs, the Rocky Mountains were developing into the ranges we know today, the ocean receded, and tropical lowlands occupied the region that today is the Great Plains. As time passed, the climate of North America became cooler and drier, and volcanic activity in the western United States produced enormous amounts of volcanic ash that was blown eastward. Ash-mantled plains were home to great herds of plant-eating mammals and their predators. Like the savannas of east Africa today, the rich volcanic soils supported grasses, which, together with small trees and bushes growing along shallow streams, were a ready food source for grass- and leaf-eaters. Many of the animals that thrived and lived here became reliant upon the moderate climate for survival and their numbers expanded to the capacity of the available food supply.

As time passed, however, the climate became more arid. To the west, the Rocky Mountains continued to rise, and the flow of moisture-laden air from the west was interrupted. With less rain came plants that could survive on less water. Drought became commonplace. Over the years streams dried up and even the grasses withered. Water-dependent animals were drawn to waterholes in the stream beds, and they congregated at these places between periods of feeding on the diminishing vegetation. Large animals, such as the rhinoceros and chalicothere Moropus, a distant relative of the horse, were finally unable to travel far enough away to find fresh forage and died in the shallow water of the few remaining ponds. Hundreds and thousands of some species died, littering the area around and in the waterholes with their remains. In time, the rains returned, the streams filled, and the process of burial began. Silt, sand, and ash covered the remains, burying them under several feet of wind- and stream-transported sediment.

Photo of hills at Agate Fossil Beds

-The beds, named for their proximity to rock formations containing agate, are under the grass-covered Carnegie and University Hills. From the summits of these hills, named by early collecting parties, can be seen the lazy meanders of the Niobrara River, 200 feet below.-

Early pioneers of scientific research in the West centered many of their activities here. Captain James H. Cook was the first white man to discover fossil bones at Agate Fossil Beds around 1878. Since then, bones from the site have been exhibited throughout the world. Captain Cook and his son, Harold, made Agate Springs Ranch a headquarters for paleontologists and acquired an excellent fossil collection.

Agate Fossil Beds Today
Scientists estimate that at least 75 percent of the fossil-bearing parts of the hills are unquarried. The Miocene fossil mammal bones are extremely abundant (comprising a variety of different species), and are remarkably well preserved, with numerous complete skeletons.

Future Development of Agate Fossil Beds
The best view of the Agate fossils is in the Visitor Center and Museum life-sized exhibits, though the quarries and accompanying wayside exhibits can be visited along park trails. New trails around the fossil deposits and quarries will be designed and constructed in the future, giving visitors a firsthand sense of the paleontological history of the park. Exposed fossils and their enclosing sediments weather quickly in the rigorous High Plains climate of northwestern Nebraska. Because of this, and the apparent scientific redundancy of the dense Agate bone bed, only selected representative portions of that bone bed (e.g., Beardog Hill) are planned for seasonal excavation and exposure.

Geology of the Fossil Site
The Agate site contains an outstanding record of a chapter of evolution frequently referred to as the "Age of Mammals" because of the tremendous increase in both species and numbers of mammals during that period.

All of Agate's fossil deposits are found in what geologists call the Arikaree Group of the Miocene Epoch, which spanned the period from 25 to 13 million years ago. The group is in turn divided into three formations: the Gering, Monroe Creek, and Harrison formations. The Harrison beds contain practically all of the known fossils at this site. The sedimentary rocks of this group are principally sandstone. The quarries are in the upper part of the Harrison, and the devil's corkscrews (casts of ancient beaver burrows) are in the lower part, which was laid down perhaps a million or more years before the upper part of the formation.

Illustration of menoceras
By far the most common mammal at Agate Fossil Beds was the Menoceras, a two-horned rhinoceros. This fleet-footed grazer was smaller than a Shetland pony and roamed the plains in numbers as great as the bison once did.

Illustration of moropus
The most unusual looking animal was the Moropus, a large, heavily built mammal about seven feet at the shoulders. The head was horse-like, the neck suggested faintly a giraffe, the torso a tapir, the front legs a rhinoceros, and the hind legs a bear. Most unusual were the feet, which were armed with large claw-like hooves possibly used for defense and for digging up roots and bulbs.

Illustration of dinohyus

Perhaps the most ferocious was the Dinohyus, or "Terrible Pig" - a monstrous beast more than seven feet tall at the shoulders and about ten feet long. It had a massive head with large tusks and a small brain. However, unlike the domestic pig, its legs were quite long and slender.

Illustration of stenomylus
Large herds of a delicate, graceful litte mammal, the Stenomylus, roamed the Miocene plains. It was slightly over two feet tall and had long, slender legs and deerlike hooves.

Fragments of fossils have been found of many other animals that lived here during the Miocene Epoch.

The Fossil-Collecting Story
In the summer of 1904, O.A. Peterson of the Carnegie Museum at Pittsburgh came to Agate, and with the able assistance of Harold Cook, then 17, conducted the first scientific excavation at this site. They discovered a rich quarry, containing a type of rhinoceros that was new to science.

In 1905, Professor E.H. Barbour and four students of the University of Nebraska opened a quarry in the side of University Hill. Both the Carnegie Museum and the University of Nebraska worked their respective quarries for a number of collecting seasons. Yale University also collected at the quarries about the same time.

In 1906, Professor E.B. Loomis and a party from Amherst College joined the collectors. They excavated in a small hill which Loomis called Amherst Point. Returning in 1907 and again in 1908, the Loomis party discovered a quarry of Stenomylus skeletons. Approximately 18 skulls, together with enough scattered bones to complete the skeletons, were collected from one pocket. In an adjacent area, three complete skeletons were found.

In 1909, the Carnegie Museum removed at least 40 skeletons. The American Museum of Natural History collected here for about 20 years, starting in 1910.

Several other institutions sent collecting parties to Agate in later years. Although no sites are currently being excavated, visitors are welcome at sites when the paleontologists are working.

park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A geology photo album for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

geologic research subheading

Information about the park's research program is available on the park's research webpage.

For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

selected links subheading
Park Highlights

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

Currently, we do not have a listing for any park-specific geology education programs or activities.

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www.nature.nps.gov/geology/parks/agfo/index.cfm   I  Email: Webmaster
This site is best viewed in Internet Explorer 6.0 or Netscape 7.0