The rugged landscape of Oregon was shaped over millions of years. Fire, floods, earthquakes and volcanic eruptions — driven by the collision of an oceanic and continental plate — each had a hand in helping to shape this beautiful part of the world. The ground here has been moving and shifting on a steady northeast direction for several hundred million years and continues today.
Oregon's geologic record extends back to the Devonian. Oregon had been mostly submerged hidden beneath the depths of an ancient ocean. The centre of the state boasts the oldest rocks. Near Suplee, Oregon snuggled up against the Malheur National Forest you can find Devonian limestones with a lovely of shallow-water marine invertebrates. Look for corals and brachiopod who made a living in Devonian seas far from where they rest today.
In the Carboniferous period, a series of volcanic archipelagos formed in Oregon. The islands enjoyed a warm, wet, terrestrial environments. Think of the Mississipi today. Fossils in Oregon's oldest floral assemblage, dating to the Late Carboniferous, were built on a lagoon ecosystem. The fossil fauna here include horsetails, ferns, scale trees, and conifer tree seeds. Formations of similar age also include shallow-water invertebrates telling us that Oregon's volcanic islands were surrounded by coral reefs.
Oregon remained mostly submerged until the Paleocene. Oregon was covered by seaways and volcanic islands during the Mesozoic. We find marine plants, invertebrates, ichthyosaurs, pterosaurs, and traces such as invertebrate burrows.
During the Cenozoic, Oregon's climate gradually cooled and eventually yielded the environments now found in the state. The era's fossils include marine and terrestrial plants, invertebrates, fish, amphibians, turtles, birds, mammals, and traces such as eggs and animal tracks.
Sediment records show that Oregon remained mostly submerged until the Paleocene period. The state's earliest fossil record includes plants, corals, and conodonts.
Oregon was covered by seaways and volcanic islands during the Mesozoic era. Fossils from this period include marine plants, invertebrates, ichthyosaurs, pterosaurs, and traces such as invertebrate burrows.
During the Cenozoic, Oregon's climate gradually cooled and eventually yielded the environments now found in the state. The era's fossils include marine and terrestrial plants, invertebrates, fish, amphibians, turtles, birds, mammals, and traces such as eggs and animal tracks.
Reference: https://www.oregongeology.org/pubs/ims/ims-028/index.htm
