In 1988, the Hagerman horse became Idaho's state fossil and Hagerman Fossil Beds became a national monument. The Monument contains the Hagerman Horse Quarry, a national natural landmark, recognized as one of the six most important sites in the world regarding the fossil history of horses.
Hagerman Fossil Beds is nationally and internationally significant for its world-class paleontological resources. It includes the world's richest fossil deposits, in quality, quantity, and diversity from the late Pliocene epoch. Many of its fossils represent the last vestiges of species that existed before the last Ice Age, the Pleistocene, and the earliest modern flora and fauna.
The Monument's paleontological resources are contained in a continuous, undisturbed stratigraphic record spanning at least 500,000 years. The fossils deposited here appear to represent an entire paleontological ecosystem with a variety of habitats such as wetland, riparian, and grassland savanna. Most of the fossils contained in the park are not obvious. There are no hikes or observation areas to see the fossils in place. A sampling of excavated fossils is displayed in the park visitor center, while the other fossils (most of small size and limited scope) are studied under laboratory conditions not currently visible to park visitors. It is in the long term plans for the park to make the laboratory work and procedures more accessible to everyone.
The Monument is also one of four National Park system units containing a portion of the Oregon Trail National Historic Trail. Ruts from the wagons that used the Trail are visible from one of the marked lookout points inside the park grounds.