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3. Early Sediments: Oregon's first coast

Exotic Terranes
(Lighter shading indicates original extent.)

As the Exotic Terranessee Unit 1 settled into position and were fused in place by the hot Batholiths and Plutonssee Unit 2, sedimentary rocks began to be deposited in what is now Oregon. Starting about 130 million years ago, rocks made of sand and mud were forming along Oregon’s first coastline, which stretched northeast across the state from Grants Pass to Pendleton. Coal beds from these ancient coastal swamps and ammonite fossils from these rocks remind us that this was the age of the dinosaurs.

OGDC units: shallow marine deltaic and terrestrial sedimentary rocks of the Jurassic-Cretaceous Myrtle Group, Cretaceous Mitchell Group and Hornbrook Formation, Paleocene Herren and Payne Cliffs Formations

Age Range: 130 million to 50 million years ago
Rock Types: sandstone, shale, conglomerate
Did You Know? Fossils from the Early Sediments include icthyosaurs, pteranodons, and ammonites, but no dinosaur bones have been found in Oregon yet!


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