Republic Graben

The Republic Graben, named after the town of Republic, Washington, is one of a number of Eocene extensional basins in what is now the Okanogan Highland. Having been downdropped it preserves a thick section of volcanic and minor volcaniclastic rocks (Sanpoil Volcanics, mainly rhyodacite) as well as fossiliferous lacustrine deposits. The volcanic rocks represent the eruptive cover of the widespread Eocene granitic intrusions in the region, and formerly must have been much more widespread.

Base and precious metal deposits are widespread in the graben.

The graben projects to the south-southwest under the Miocene basalts in the Columbia Plateau.

References

• Alt, David D.; Hyndman, Donald (2008). "Washington 20: Tonasket-Colville-Tiger". Roadside Geology of Washington. Missoula, MT: Mountain Press Publishing Company. pp. 32–33, 50. ISBN 0-87842-160-2.
• The Okanogan Highlands
• North Central Washington Field Trip Guide