Fossils of the Columbia Plateau

Paleozoic fossils

The fossil brachiopod Titanaria is found in Mississippian rocks in northern California (Baird Shale, Shasta County) and central Oregon (Coffee Creek Formation) and is among the largest brachiopods in the world. Titanaria's shell reached widths (along the hinge line) of more than 35 centimeters (14 inches). 

Mesozoic fossils

During the Jurassic and part of the Cretaceous, ammonoid cephalopods and bivalves were abundant and diverse in the shallow sea that covered this region. Vertebrate fossils are found occasionally, including sea crocodiles and pterosaurs.

Cenozoic fossils

Several sites in Oregon and Washington preserve abundant Cenozoic terrestrial fossils, especially plants and mammals, as a result of widespread volcanic activity in the area. During the Neogene, the Columbia Plateau was covered in large volcanic outflows of flood basalt. These outflows are associated with the same hot spot that now heats Yellowstone National Park. Some of these lava flows overran forests, leaving behind empty molds of trees.

At some localities, such as Ginkgo Petrified Forest State Park in Washington, petrified (permineralized) wood has been preserved either by burial within lake sediments or in volcanic mudflows. Examples of petrified wood types preserved in this region include ginkgo, conifers (pine, Douglas fir, bald-cypress-like), and many angiosperms (sycamore, sweet gum, alder, elm, tupelo, hickory, oak, and cherry).

John Day Fossil Beds

The Eocene to Miocene Clarno, John Day, and Mascall formations are collectively known as the John Day Fossil Beds. They span over 40 million years and can be best seen in and around John Day Fossil Beds National Monument in Wheeler and Grant Counties in north-central Oregon.

Eocene Clarno Formation

The Eocene Clarno Formation, exposed at several sites in central Oregon, consists of a series of volcanic ash deposits, which quickly buried plants and animals and protected them from decomposition. The resulting spectacular fossils include hundreds of kinds of leaves and seeds, as well as insects, mammals, and other animals. The famous Clarno “nut beds” exposed in Wheeler County in north-central Oregon have yielded more than 170 species of fossil fruits and seeds. Clarno fossil leaves include palms, bananas, and many flowering tree species. These fossils indicate that between 50 and 44 million years ago, the climate of what is now the Pacific Northwest was warm and humid.

Oligocene John Day Formation

The Oligocene John Day Formation is another series of volcanic ash layers rich in fossil plants and animals, which formed between 35 and 25 million years ago. The climate was cooler, but species diversity was still high.

Fossils found in the John Day Formation include more than 60 species of plants, including the “dawn redwood” (Metasequoia), a relative of the living giant sequoias (Sequoiadendron gigantea) and coast redwoods (Sequoia sempervirens). Although dawn redwoods where once widespread in the northern hemisphere, China is the only country where they grow in the wild today. Dawn redwood differs from both giant sequoias and the coast redwood in that it is deciduous (meaning that it loses its leaves seasonally rather than remaining evergreen like most conifers). Examples of other plants from the John Day Formation include alder (Alnus), hornbeam (Paracarpinus), katsura (Cercidiphyllum), maple (Acer), and oak (Quercus).

The John Day Formation also contains more than 100 species of mammals, including entelodonts ("hell pigs"), oreodonts, other artiodactyls (even-toed hoofed mammals), nimravids (false saber-toothed cats), horses, rhinoceroses, camels, and rodents.

Miocene Mascall Formation

Following the eruption of the Columbia River Basalt flows, between 17 and 12 million years ago, further ashfalls from eruptions in the Cascades formed the early to middle Miocene Mascall Formation. The Mascall Formation preserves another diverse assemblage of mammals, including horses, camels, rhinoceroses, bears, pronghorn, deer, weasels, raccoons, cats, and mastodonts. Plant fossils include ginkgo, dawn redwood, oak, sycamore, hackberry, maple, and elm, reflect the region’s cooling climate during this time period.

The flood basalts also contain one of the world’s most unusual fossils, the “Blue Lake Rhino,” in Grant County, Washington. It is an external mold of a rhinoceros, which lived around 14.5 million years ago. It apparently formed when lava flowed into the water, forming pillows. These were still hot enough to be soft but not hot enough to completely burn away the body.

Miocene Rattlesnake Formation

The youngest fossil-bearing unit at John Day Fossil Beds is the Rattlesnake Formation, which dates to the late Miocene, about 7 million years ago. As with the older rock units, it preserves a diverse mammal fauna. These include animals like rodents, camels, horses, peccaries, rhinoceroses, shovel-tuskers (elephant-like animals), foxes, and short-faced bears. The world's oldest fisher (Pekania occulta), a type of mustelid (a group including weasels and skunks), has been recorded from this formation. 

Quaternary fossils

Large mammals, including woolly mammoths and camels dating from the Quaternary, have been found in a variety of locations representing ancient riverbanks and lakes. The oldest known mastodon (another relative of modern elephants) in North America comes from the Ringold Formation at White Bluffs in south-central Washington.