Columbia River Basalt Province, Washington and Oregon

Flood basalt volcanism

Grande Ronde flows of the Columbia River Basalt Group exposed in the Grande Ronde Valley near Anatone, Washington.


Grande Ronde flows of the Columbia River Basalt Group exposed in Joseph Canyon, Oregon.


Grande Ronde basalts cut by feeder dikes in Joseph Canyon; dikes can be distinguished from the surrounding country rock by horizontal columnar jointing.


A swarm of feeder dikes cuts Grande Ronde flows of the Columbia River Basalt Group.


Horizontal bands on the surface of Grande Ronde basalt column mark the progress of column formation by repeated fracture propagation perpendicular to the length of the column.