The Pacific floor is still being subducted about 50 miles off the coast. The sediments are still being scraped off. The present coast range is being uplifted.

Oregon is the product of glancing collisions of continental and Pacific ocean plates. Currently the North American plate moves west and somewhat south. The entire Pacific plate is moving north which is helping tear the Juan de Fuca Rift.

Most recently, steam continues to vent and earthquakes present.

Renditions of the animals around middle late Eocene from the Clarno unit.

This shows the volcanic activity in the big picture. The Columbia River Basalt group represents a series of volcanic eruptions. These were flood basalts that covered a vast area of the NW flowing from Idaho all the way to the Pacific at times. Not one event but many. The basalts are from a few to thousands of feet thick.

We can see the CRB in the gorge and in the Willamette but also along our route to John Day. Evidenced by thick relatively flat layers of basalt often times with columnar jointing. Note in the next slide.

About 200 mya, the continental shelf appears to have been at an angle from the northeast corner of the state to the Klamaths. The initiation of the collision of the Juan de Fuca plate may have begun at the time of the separation of North America from Europe. As the ocean floor began to sink beneath the continent, the coastal plain and shelf sediments were scraped off against the edge of the continent and formed as a coastal range, the Blue Mountains and the Wallowa Mtns. and in the Klamath area (only a small part of the original Klamath remains). This scraping (including an occasional seafloor scrap) is jumbled and almost unrecognizable “confused heap.”

Sea floor subduction yields the scraping for coastal ranges and these are paralleled by a series of volcanoes. As the Cascades today parallel the coast range so 200 mya did volcanoes parallel the coastal ranges of that time. These volcanoes are now eroded. The evidence of old volcanic include granitic masses. Why? Old molten magmas moving up through sediments (coastal) from deep below the surface melt the sediments, mix, change melting point, and the new magma has a more graniitc mix. As the magma erupts, one gets an andesite – as it cools below you get a settling of crystals and differential crystallization yielding a more granitic/dioritic rock. So masses of granitic rock are the remnants of the great magma reservoirs of the former Cascades. Also old sediments are composed of volcanic debris. This situation lasted from between 200 mya to about 150 mya up until about 30 mya (through the Mesozoic and beyond). The seafloor moved toward the continent and everything marched to the sea. The continent built out as the seafloor was subducted. As the coastal range moved out so too did the volcanic chain. The chain of coastal mountains is buried today under more recent volcanism. Remnants high enough yet to see are  in the Blue, Wallowa, and Klamath mountains. The bay out to the west of the then coastal range accumulated sediment from the range.

The sediments/coastal ranges other than Blue etc. may have always been submerged such that the volcanic chain may have been on the coast or even an island chain. Evidence of this can be seen from about 40 mya. Something changed about 35 mya when the subduction line straightened and paralleled what has become today’s coastline. Volcanics shifted from curve to present day line parallel to the coast. The shift meant that the former subduction area stabilized to a new platform. The activity of these early Cascades lasted for about 10 my. These were explosive eruptions which spread light colored ash over much of central Oregon. About 20 to 25 mya, the Cascades took a breather and a new eruption occurred in central and then eastern Oregon. Floods of basalt covered thousands of square miles. Then the basalt floods stopped about 12 mya and the volcanic activity resumed in the Cascades. Why? Did the slab of ocean crust break off? Faulting and fracturing in south central and southeast Oregon occurred from starting between 10 and 15 mya up to the present. The west part of the state is moving north relative  to the rest of the state. It seems that the floor of the Pacific is moving north and dragging the western part of the continent with it (as we see with the San Andreas Fault in Southern California) But in northern California and Oregon it is not a narrow strip but a broad zone. This could be due to the Juan de Fuca ridge.

This is a geologic map showing the area of John Day. Formations are layers of rock that are identifiable across large areas and formed near the same time. The list of formations is always from the youngest down to the oldest. Miocene is a range of time about 11 to 25 mya. Eocene is older about 40 to 50 mya range. Mesozoic and Paleozoic are older longer time periods.

Here is a geologic column from the John Day area from the upper Clarno formation in the Eocene time. We can see the various layers that form the formation and their thicknesses. We also see characteristic fossils found at the different levels. This informs us about the age of the rock and the fossils. It also tells us about the climate at the time.

This cave is the result of volcanism during the Pliocene or Pleistocene time (within the last 13 million years). “Tubes and tunnels in basalt occur as molten lava cools to form a solid crust on the surface even as the hot lava stream continues to run out deep in the flow. As volcanic activity producing the lava ceases, the tube is drained leaving the cave or cavern.” For the tunnel to form the lava needs to be thick and syrupy and are most often found in pahoehoe flows. Malheur cave intersects the water table and so creates an underground lake.

Diamond Craters Lava Field is called “one of the most dramatic of Oregon’s volcanic attractions, displaying a varied landscape produced by late Miocene to Pleistocene eruptions.” (about 9 million years ago this began and continued to about 2 mya.) Named for the diamond shaped cattle brand owned by an early settler. Within 22 sq miles there are over 100 cinder cones and craters. About 9 mya vents in the area opened and spewed out enough ash and lava to cover 7000 sq miles up to 130 ft thick. About 2500 years ago there were a number of eplosions and intrusions forming cinder cones and vast new lava flows. This bowed the ground surface forming domes.

Pahoehoe looks like a lava fall rippling over the edge of small cliffs. Channels and tubes are abundant in such flows.