Fossils of the 2025 National Fossil Day Artwork (U.S. National Park Service)

John Day Fossil Beds National Monument: 45 Million Years of Mammalian Menageries

Art work poster of prehistoric scene with animals and plants reconstructed from the fossil record

Today, the badlands, sagebrush steppe, and riparian habitats of the John Day River Basin of eastern and central Oregon support diverse systems of plants and animals. Beneath the surfaces, the rocks and deposits include evidence of many millions of years of living things that came before, shaping those modern systems. There is an unparalleled record here telling the stories of how life in their environments has changed during the Cenozoic Era, from the Eocene Epoch to the late Miocene Epoch in northwestern United States. Paleontologists from many institutions have been delving into the rocks and fossils of the John Day Basin for more than 160 years to understand this history of life. In recognition of these fossil resources, John Day Fossil Beds National Monument (JODA) was established on October 8, 1975 and is administered by the National Park Service. Today it encompasses 13,944 acres, divided among three units: Sheep Rock, Painted Hills, and Clarno. The monument only preserves a fraction of the overall John Day fossil beds, requiring the NPS to partner with other federal, state, and tribal partners, and private landowners. An average of 210,000 visitors annually visits the lands of the monument for outdoor recreation and to learn about the 45 million years of fossil heritage preserved within the region. New discoveries are still being made here by National Park Service paleontologists and their colleagues. For the 2025 National Fossil Day Logo, we feature the 29-million-year-old Oligocene assemblage of the Turtle Cove Member of the John Day Formation, inspired by new and old discoveries made at John Day Fossil Beds National Monument.

Photo of hills with layered bands of rock — The colorful badlands of John Day Fossil Bed National Monument, Oregon.
NPS photo.

The geologic history of John Day Fossil Beds National Monument actually extends into the Cretaceous Period and records a series of events of volcanic activity and sedimentary erosional accumulation. The oldest rocks within the monument are of the Late Cretaceous Gable Creek Formation and preserve a large river mouth grading into a shallow coastal environment. However, few fossils (primarily wood fragments) have been identified within the monument from this geologic horizon. Most of what is known from fossils comes from the Cenozoic rocks.

The Eocene Epoch of John Day Fossil Beds National Monument records a time when western North America was experiencing widespread volcanic activities. The oldest Eocene rocks of John Day Fossil Beds are part of the Clarno Formation, which shows lava flows, fast-moving volcanic debris flows called lahars, and evidence of rivers and lakes with mudstones, shales, and conglomerates. These rivers cut through a semitropical forest known from fossil evidence of at least 77 species of plants represented by fossilized seeds, nuts, fruits and wood. Animals from the Clarno Formation included some of the first large mammals, such as rhino-like brontotheres, small early multi-toed horses, and an early large bear-sized carnivore.

The Oligocene Epoch at the monument is represented by the John Day Formation, which is one of the more fossiliferous geologic horizons within the monument. Broken down into seven fossil-bearing rock units, these rocks record life between 39 and 18 million years ago. The oldest part of the John Day Formation is the Bridge Creek Flora (Big Basin Member), which contains shales that preserve leaves, insects, fish, and amphibian fossils as well as colorful paleosols (fossil soils) of the Painted Hills. Above this member is the Turtle Cove Member, which has layers of ash flows and claystones that preserve unique and unusual fossils of an ancient forest of the Pacific Northwest. The Turtle Cove Member is the main assemblage in the 2025 National Fossil Day art discussed below. Above the Turtle Cove Member are the Kimberly, Haystack Valley, Balm Creek, Johnson Canyon, and Rose Creek Members which preserve floodplain habitats that were covered by volcanic ash. All of these members have preserved extensive mammal fossils.

Lastly, the Miocene Epoch at the monument is represented by several geologic units, beginning with the 16-million-year-old Picture Gorge Basalts. The basalts come from a major volcanic event, made up of 61 lava flows that were erupted on an average interval of 15 thousand years per flow over the course of about 1 million years. These flows covered 2500 square miles in basaltic lava. As this volcanic episode was ending, minor volcanic activity and the formation of lakes and streams in floodplains began the deposition of the Mascall Formation. The Mascall Formation was deposited between about 16 and 14 million years ago. It shows another time of mammals diversifying with forms such as long-jawed gomphotheres (elephant relatives), early dogs, bear-dogs, weasels, cats, pronghorns, camels, rhinos, and horses. At the top of the monument’s bedrock is the Rattlesnake Formation, formed around 8 to 5 million years ago by another series of volcanic ash and debris flow events. Just prior to the volcanism, large mammals such as ground sloths, one-toed horses, sabretooth cats, peccaries, North America’s last rhinos, and single-toed horses roamed the region.

The Oligocene: A Time of Transition

The Oligocene Epoch occurred approximately 34 million years to 23 million years. During this time there was a gradual change from the nearly tropical wet and warm world of the Eocene Epoch, with forests nearly worldwide (including Antarctica), to the drier and cooler climate that promoted the open woodland and grassland habitats that evolved during the Miocene Epoch. The 2025 National Fossil Day Artwork depicts the flora and fauna of the Turtle Cove Member of the John Day Formation, which marks the beginning of the Pacific Northwest’s transition from a forest-dominated habitat to a more open woodland, and eventually to open sagebrush steppe. The unique plants and animals depicted in this piece offer clues to this environmental transition.

Painted mural of prehistoric scene with plants and animals — The Oligocene Turtle Cove Member fauna and flora assemblage of the John Day Formation from John Day Fossil Beds National Monument.
Roger Witter/NPS

America’s Last Primates

During the Paleocene, Eocene and Oligocene Epochs (66–25 million years ago), lemur-like primates known as adapiformes roamed throughout North America. However, most of these early primates went extinct by the end of the Eocene. A few species survived as late as the early Miocene in North America. One such species, Ekgmowechashala zancanellai, was unique to the Oligocene Turtle Cove Member of John Day Fossil Beds National Monument. Fossils of Ekgmowechashala (“little cat man” in Sioux) have also been found in South Dakota, Nebraska, and Texas. It was a small lemur-like primate with teeth specialized to eat soft fruits and insects. We depict Ekgmowechashala within a fruiting hackberry tree near a grasshopper. Both the tree and the insect have fossil representation at the monument: leaves and seeds from the hackberry, and the first ever fossilized egg clutch from the grasshopper. The presence of the primate Ekgmowechashala provides evidence that forests were still a dominant feature in the Pacific Northwest during the Oligocene of the Turtle Cove Member of the John Day Formation.

Line-art drawing of a small prehistoric mammal and detail showing 3 teeth — Left: The teeth of the lower jaw of *Ekgmowechashala zancanellai*. Right: A restoration of *Ekgmowechashala zancanellai*.
NPS/art by Benji Paysnoe.

Hooves on the Move

Ungulate (hoofed) mammals are well-represented at John Day Fossil Beds National Monument throughout the Eocene, Oligocene, and Miocene rocks and sediments within the monument. Hoofed mammals are divided into two major groups: artiodactyls, which have an even number of toes; and perissodactyls, which have an odd number of toes. The Turtle Cove Member of the John Day Formation had numerous ungulate mammals that include artiodactyls such as peccaries, camels, early deer-like mammals, oreodonts (a group of mammals with features similar to both pigs and camels), and a giant omnivore called an entelodont. Perissodactyls from the Turtle Cove Member include three-toed horses and rhinos. The 2025 National Fossil Day Art features two perissodactyls, the three-toed horse Miohippus annectens and the two-horn rhino Diceratherium annectens. Miohippus annectens was a small horse that had an adult weight between 25 to 30 kg and evolved into lineages with traits suited for either forest or open grasslands. Thomas Condon, the foundational figure of John Day Basin paleontology, sent Miohippus fossils to Othniel Charles Marsh (of “Bone Wars” fame), who in turn wrote to Charles Darwin about how these fossils supported Darwin’s theory of evolution. Diceratherium annectens was an early rhino that evolved two horns side-by-side on the end of its nose.

Two images: fossil skull of prehistoric miohippus and an artist's rendition of two animals — Left: The skull of *Miohippus*. Right: Two *Miohippus* from the Turtle Cove Member of the John Day Formation at John Day Fossil Beds.
NPS images.

Two photos: fossil bones in rock matrix and a reconstructed fossil skeleton — Left: The skull and rear limb bones of *Diceratherium* from the Turtle Cove Member of the John Day Formation at John Day Fossil Beds. Right: The mounted skeleton of *Diceratherium*.
NPS photos.

False Cats and Little Big Eared Dogs

Mammalian carnivores (Order Carnivora) are also well-represented within the Eocene, Oligocene, and Miocene of John Day Fossil Beds National Monument. Fossils of early relatives of dogs, weasels, racoons, bears, and cats are typical within these sedimentary rocks, but there are also extinct groups such as false cats, bear-dogs, and other groups that are even farther removed from modern carnivorans. The 2025 National Fossil Day Art features two carnivorans from the Turtle Cove Member of the John Day Formation: the false sabertoothed cat Nimravus brachyops and the little “bone crushing” dog Cynarctoides lemur. False sabertoothed cats, or nimravids were early members of the group that includes modern true cats, hyenas, civets, and mongooses. Nimravids evolved short cat-like skulls, with many species having sabertooth adaptations. A telltale difference can be found in their skulls: unlike true cats, nimravids did not have complete bony walls around their ear canals (auditory bullae, the paired bumps at the underside of the base of the skull in cats and many other mammals). Instead, they probably had cartilage like modern civets. Nimravus brachyops was a leopard-like nimravid with short saber-like upper canine teeth. Like a leopard, it was adapted to both hunt in forested and open habitats for prey, such as Miohippus. The little “bone crushing” dog Cynarctoides lemur was a small racoon-like canid that most likely hunted for prey or consumed fruits and nuts. The “bone crushing” title comes from the subfamily of dogs Cynarctoides belonged to called the borophagines. This group evolved robust cheek teeth, which ultimately led to some species being able to crack bones like today’s hyenas. Cynarctoides also had enlarged structures around the ears, suggesting it would have large ears similar to today’s fennec and bat-eared foxes of Africa. Like these foxes, Cynarctoides used its excellent hearing to track down prey such as insects, small reptiles, and rodents.