Columbia Plateau
(Oregon & Washington & Parts of Idaho & Utah )
Overview
The Columbia Plateau is dominated by Miocene flood‑basalt flows, ash layers, and river/lake deposits. Fossils range from Trilobites to Ice‑Age Megafauna like the Mammoth. Key localities include the Clarno & John Day Fossil Beds (Eocene–Miocene) and Ringold Formation (Pleistocene).
Signature Fossils by Era & Group
Paleozoic
- Mississippian (Carboniferous)
Mammal – none recorded
Reptile – none recorded
Invertebrate – giant brachiopod Titanaria (>35 cm)
Mesozoic
- Jurassic
Reptile – marine “sea crocodile” Zoneait (Snowshoe Fm.)
Invertebrate – abundant ammonoids & bivalves - Cretaceous
Reptile – pterosaur Bennettazhia (Oregon)
Cenozoic
- Eocene (Clarno Fm.)
Mammal – rhino‑relative Zaisanamynodon
Plant – tropical nuts & leaves (palms, bananas) - Oligocene (John Day Fm.)
Mammal – “hell pig” Entelodont, saber‑toothed nimravids, early dogs
Plant – dawn redwood Metasequoia, alder, maple - Miocene (Mascall & Rattlesnake Fm.)
Mammal – horse Archaeohippus, bear‑dog Amphicyon, gomphothere elephants, short‑faced bear
Plant – ginkgo, hackberry seeds
Special – “Blue Lake Rhino” lava mold - Pleistocene (Ringold Fm.)
Mammal – woolly mammoth (Mammuthus) tracks, mastodon, extinct camel Camelops
Gallery
Rock Units
Flood‑basalt lavas (Columbia River Basalt Group) dominate bedrock, interlayered with fossil‑rich ash + lake sediments. Key formations: Clarno (Eocene ash), John Day (Oligocene ash), Mascall & Rattlesnake (Miocene ash & river gravels), Ringold (Pliocene–Pleistocene river/lake).