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7. Coast Range Volcanoes: Oregon's first hot spot

Exotic Terranes
(Lighter shading indicates original extent.)

A few million years after the Siletz Terranesee Unit 4 joined the continent and began to be buried by sand and mud, the newly formed northwest corner of Oregon, moving with the North American continent, drifted west across a hot spot, triggering huge eruptions of lava that built up along the coast. For several million years the hot spot fed magma from deep within the Earth into the layer of marine sedimentary rocks (Coast Range Sedimentssee Unit 6) that was growing on the ocean floor. Today these volcanic and intrusive rocks make up the Tillamook Highlands and some of Oregon’s most famous coastal landmarks, including Cascade Head and Cape Perpetua

OGDC units: mafic intrusive and volcanic rocks of the Eocene Grays River Volcanics, Mary’s Peak Intrusives, Tillamook Volcanics, Yachats Basalt, basalt of Cannery Hill, basalt of Waverly Heights, basalt of Cascade Head and diabase of Lee’s Falls

Age Range: 45 million to 36 million years ago
Rock Types: basalt, diabase
Did You Know? Mary’s Peak, the highest point in the Coast Range (4,097 ft), is supported by resistant intrusive basalt of the Coast Range Volcanoes.
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Heceta Head State Park
Neptune State Park


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