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FOUNDATION PHASE -

2. Batholiths and Plutons: mortar for the foundation

Exotic Terranes
(Lighter shading indicates original extent.)

As the Exotic Terranessee Unit 1 were plastered onto the edge of the North American continent, magma from deep within Earth was injected into them and then cooled. The magma formed large masses of granite and related rocks called batholiths and smaller blobs called plutons. Some of the rocks that form the larger batholiths can be seen in the Wallowa and Elkhorn Mountains of northeast Oregon and near Grants Pass and Medford in southwest Oregon. These intrusive igneous rocks appear to be the first rocks that truly originated in Oregon.

OGDC units: Jurassic-Cretaceous Bald Mountain and Wallowa batholiths Pedro Mountain, North Fork and Sunrise Butte stocks in northeastern Oregon; Buckskin Peak, Gold Hill, Grants Pass, Grayback, and Jacksonville plutons in southwest Oregon

Age Range: 165 million to 130 million years
Rock Types: granodiorite, granite, gabbro, diorite, tonalite, quartz diorite
Did You Know? A water well in the Grants Pass pluton acts like a seismograph by rising and falling when large earthquakes occur even far away.
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Mount Ashland ski area
Anthony Lakes ski area

 

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