The Oregon-Idaho graben evolved after widespread Uwleiitic flood basalt volcanism associated with the arrival of the
plume head of the Yellowstone hotspot beneath southeastern Oregon approximately 17-16 Ma. The north- to north- northeast-trending, 50 km-wide graben evolved between 15.5 and 10.5 Ma during east-west extension. The graben is part
of a middle Miocene back-arc rift (1,100 km long) that includes the northern Nevada rift, the Baker and LaGrande
grabens, and the Chief Joseph dike swarm of the Columbia River Basalt Group. The graben ceased to be a volcano- tectonic depression as the cross-cutting western Snake River plain began to evolve at approximately 10.5 Ma.