Date of this Version
Graham, J. 2009. Agate Fossil Beds National Monument Geologic Resources Inventory Report.
Natural Resource Report NPS/NRPC/GRD/NRR—2009/080. National Park Service, Denver, Colorado.
This report accompanies the digital geologic map for Agate Fossil Beds National Monument in Nebraska, which the Geologic Resources Division produced in collaboration with its partners. It contains information relevant to resource management and scientific research. This document incorporates preexisting geologic information and does not include new data or additional fieldwork.
Formerly a working ranch in sparsely populated northwestern Nebraska, Agate Fossil Beds National Monument is one of the most important paleontological sites in the world for studying Miocene-age mammals and the evolving Miocene world which existed around 20 million years ago. The main bonebeds at Carnegie Hill and University Hill (collectively known as ‘Fossil Hills’) were the first major concentrated deposits of Tertiaryage mammals discovered in North America. The bonebeds produced the most complete and bestpreserved skeletons of Dinohyus (now known as Daeodon) yet discovered. The corkscrew burrow, Daemonelix, is one of the more unusual features discovered in the Monument. The much younger fossils and burrows at Beardog Hill represent the oldest denning community of carnivores known in the fossil record. Furthermore, 100 or more of the tiny camelid, Stenomylus, were found mummified and mostly articulated in a quarry east of Fossil Hills. The fossil birds recovered from Agate Fossil Beds National Monument add to the Monument’s faunal diversity and help verify paleoenvironmental interpretations. New genera and species have been identified from the collections, including the first record of a crane, Gruiformes. Significantly, the paleoavifauna represents a worldwide fauna that has only recently been recognized at a few other localities. Protection and preservation of the extraordinary paleontological resources are primary geologic issues at the Monument. The carnivore den site at Beardog Hill and the fossils in the Stenomylus Quarry are subject to erosion, weathering, and occasional vandalism. The historic quarries at Fossil Hills are easily accessible to visitors and are not monitored. A comprehensive fossil taxa list for the Fossil Hills, Beardog Hill, and the Stenomylus Quarry could prove useful to resource managers. The fossil collections from Agate Fossil Beds National Monument continue to provide paleontologists with valuable information about the Miocene ecosystem. Further research at the Monument could include testing the east side of Carnegie Hill as well as a significant rock layer in the Stenomylus Quarry for mammal fossils. Agates, which give the park its name, are found in a thin band along ash deposits just above the Miocene bonebeds. Visitors have easy access to the agates, known for their polish and luster. Collecting agates is a legal activity in the U.S. Forest Service Oglalla National Grassland, which is located north of the park, and many visitors come to Agate Fossil Beds National Monument expecting to collect these rocks. Rockfall areas at University Hill and Carnegie Hill pose a potential hazard to both visitors and researchers. Signs have been posted warning visitors of the hazard. Exploration wells for oil and gas were drilled just south of the park more than sixty years ago to test the Agate anticline, but no oil or gas was discovered. Minimally productive wells exist about 32 km (20 mi) south of the Monument and potential exploration drilling in the area remains a minor concern for Monument management. The Miocene landscape was one of broad savannas with vast herds of plant-eating mammals and the carnivores that preyed upon them. Perhaps the Rocky Mountains blocked moisture from reaching the Great Plains of western Nebraska during the Miocene. Drought ensued and the fluctuating climate stressed the habitat of the browsers and grazers. As waterholes evaporated, the animals died, were buried, and became the fossilized deposits so treasured today by paleontologists and visitors to Agate Fossil Beds National Monument. Agate Fossil Beds National Monument is located on an area of the High Plains in the Niobrara Valley that escaped glaciation during the last glacial advance of the Pleistocene Ice Age. Because glaciers did not erode the Pleistocene and Holocene sediments, significant climatic variations during the past 12,000–15,000 years are recorded in the geomorphology, stratigraphy, and paleosols of the Niobrara Valley. The Niobrara River meanders through the park, creating 18 km (11 mi) of riverbank and riparian wetlands. The rich collection of fauna and associated paleoenvironments at Agate Fossil Beds National Monument provide a rare glimpse into the ecology of the carnivore community during the Early Miocene and significant insight into Tertiary global climate change. Specimens discovered in the fossil quarries continue to help scientists piece together the past. The great bonebed at Agate Fossil Beds National Monument remains one of the most impressive and scientifically interesting paleontological sites in North America.