Photos and captions of the Grande Ronde Basalt, northeastern Oregon/southeastern Washington.

The Grande Ronde Basalt formed the most voluminous part of the Columbia River Basalt Group, with a volume exceeding 151,000 km3. It erupted between about 16.5 to 15 Ma in what is now northeastern Oregon and southeastern Washington.

View from Chief Joseph Overlook
Multiple thin flows of the Grande Ronde Basalt as seen from Chief Joseph Overlook.


Flows of the Grande Ronde Basalt along the Grande Ronde River.


Feeder dikes along the Grande Ronde River, southwestern Washington.


Paleosol developed between flows


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