Ortley Thrust in the Columbia Gorge

The near vertical beds known locally as The Pinnacles lie on the Washington side of the Columbia River Gorge, just west of Doug’s Beach and across the Columbia from Rowena OR, and are readily visible from I-84. 

The WA Interactive Geologic Map indicates they are part of a west-verging left-lateral Ortley Thrust that emplaces older Grande Ronde basalts (right side of images and model) against younger Wanapum (or Saddle Mtn) basalts, both earlier (17.5-15 million year old) members of the Columbia River Basalt Group.

Ortley Thrust Panorama

Drag folds that are clearly evident on either side of the upturned beds in the images are consistent with a right to left thrust motion.  Continuation of the thrust across the river to the Oregon side is not clear.

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