John Day Fossil Beds National Monument
Location: Grant County, Oregon
Time: 50 to 6 million years ago, during the Tertiary period
About this Famous Find: Located in central Oregon, John Day Fossil Beds National Monument records over 40 million years of earth history, from the Eocene (45 million years ago) to the Pliocene (5 million years ago). Within its rocks we find a diverse animal and plant record. The paleontological record at John Day spans such a long time and represents so many different paleoenvironments that paleobotanist R.W. Chaney declared that no region in the world shows more complete sequences of Tertiary land populations, both plant and animal, than the John Day Basin.
The exposed rocks exposed have been divided into four geologic formations:
The Clarno Formation (5035 million years ago): Fossil nuts, seeds, fruit, leaves, branches, and roots from various plants are very well-preserved and indicate a tropical to subtropical climate. Also found are many different and strange-looking animals. Some, such as brontotheres and amynodonts, fed on plants while others, such as the hyaenadonts and early cats, fed on the herbivores.
The John Day Formation (3720 million years ago): Plant fossils indicate that as the climate cooled, deciduous forests and prairies replaced the earlier tropical forests and provided habitats for a more diverse fauna, including rhinoceroses, horses, camels, dogs, cats, pigs, oreodonts, and rodents.
The Mascall Formation (1512 million years ago): After a long period of volcanic eruptions, the resulting basalt flows eroded into fertile soils that nourished lush forests and grasslands, supporting an even greater diversity of animals, including horses, camels, deer, bears, weasels, dogs, and cats, as well as larger mammals like the gomphotheres (early elephants), rhinoceroses and bear-dogs.
The Rattlesnake Formation (86 million years ago): These coarse deposits indicate a time of grasslands, floodplains, and rivers and contain fragmented remains of horses, sloths, rhinoceroses, camels, peccaries, pronghorns, dogs, bears, and others.