Field Guide for Vertebrate Fossils of Hagerman National Monument

Type of Culminating Activity

Graduate Student Project

Graduation Date


Degree Title

Master of Science in Education, Earth Science



Major Advisor

Charles Waag


There exists a wide variety of vertebrate fossils in the Hagerman fauna. This is primarily due to the diversity of animal species, the wet paleoenvironment, rapid sedimentation, and the favorable conditions to preserve animals during late Pliocene. To date, 105 species of vertebrates have been recorded. The Horse Quarry is an area at Hagerman where the largest concentration of fossil horses has been located. Whole skeletons have been excavated from the Hagerman Horse Quarry. These skeletons have been identified as a species of horse, which is the earliest known record of Equus.

Fossils are an important part of geological history. They help paleontologists decipher the past environments, plants, and animals. The work at Hagerman has helped to piece together the environment 3.7 to 3.2 million years ago. The fossils discovered at Hagerman support our understanding of Lake Idaho and have helped connect the lake to other locations in the Pacific Northwest. Some of the fish and turtle fossils discovered at Hagerman correlate to species found in California and Nevada.

The stratigraphic sequence of layers at Hagerman are primarily fluvial, lacustrine, and flood plain deposits and range in texture from sand to clay and includes some volcanic ash layers. Approximately fifteen thousand years ago, the Bonneville Flood swept down the Snake River and exposed the stratigraphic layers that from the western side of the Hagerman Valley. Over time, runoff has deeply dissected the bluffs creating ravines in which fossils are located.

Statement of Purpose

This field guide is designed to introduce vertebrate fossils to ninth grade Earth Science classes. It provides background information on fossils, some local geology, and the Hagerman Fossil Beds National Monument. It contains a variety of activities for the classroom, a road log from Boise to Hagerman, and activities for the students while at the Monument. It is intended for ninth graders to read and use the information from this guide to understand the historical importance of the Hagerman National Monument and its contribution to geology and paleontology.

Previous Work

In 1928, a local rancher, Elmer Cook, showed some fossil bones to Dr. H.T. Sterns of the U.S. Geological Survey. The bones were passed on to Dr. J.W. Gidley at the U.S. National Museum (Smithsonian Institution), who identified them as belonging to a fossil horse. In the summer of 1929, Gidley came to Idaho and met with Sterns, to follow up on the discovery. They focused on the area where the fossils were found, an area which has become known as the Hagerman Horse quarry. Three tons of specimens were excavated in this area and sent back to Washington D. C. Most fossils were identified as a new species of an extinct horse now known as Equus simplicidens.

In 1930, Gidley returned to expand his work at the Hagerman Horse quarry. Using a team of horses, his crew removed hundreds of cubic yards of sand in order to reach the bone bed which lay 45 to 60 feet below various sediments. Several more horse fossils were uncovered as well as many other animal fossils including beaver, otter, and mastodon. In 1931, the Smithsonian group returned to Hagerman because the first two excavations had been so successful. Due to poor health, Gidley could not lead the paleontological operation, so the work was continued by Norman H. Boss. The 1931 excavation lead to the discovery of five nearly-complete horse skeletons, thirty-two skulls, and forty-eight lower jaws. In the summer of 1934, the field work at Hagerman continued under the leadership of a new curator, Dr. C.L. Gazin. That expedition led to the discovery of sixty-five skulls of the Hagerman horse and a skull of a small antelope. In addition, Gazin explored the surrounding area, locating the fossils of a small herd of peccary. From 1935 until 1949, work at the Hagerman site ceased altogether.

It was not until the 1950's and 1960's, that excavations in southern Idaho resumed. C.W. Hibbard of the University of Michigan began his work at Hagerman concentrating on rodents and other small animals rather than the larger vertebrates. Hibbard and his students literally crawled on their hands and knees over the exposures at Hagerman looking for mice teeth, jaws, and bones. Fossils were found in loose sediments formed on the bluffs by the constantly blowing winds. These areas are locally known as blowouts. Blowouts are created when the winds remove the very fine sediments of rock and sand from the bluffs, leaving exposed fossils behind on the surface.

In 1988, the Hagerman Fossil Beds National Monument was authorized by legislation to become a national monument because of its significant palentological contributions. Periodically, areas of the monument continue to be excavated. Field work is done by monument staff, volunteers, and college students. This work is overseen by the resident paleontologist, Dr. H.G. McDonald. Recent important discoveries that have been added to the collection include a camel skull Camelops and the shoulder bone of a lake cat Macheirodus hesperus (McDonald 1997).