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How did flood basalts help form the Columbia Plateau?

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A car drives along the Trans-Canada Highway with Mount Sir Donald's sharp, snow-capped peak rising above forested slopes in the Selkirk Mountains, British Columbia. — mountain Mount Sir Donald in the Selkirk Mountains, British Columbia, looms above a segment of the Trans-Canada Highway.

The Columbia Plateau was formed through the accumulation of extensive lava flows known as flood basalts, which buried the preexisting terrain.1

These volcanic eruptions, which occurred approximately 14 to 17 million years ago, are often associated with hot spots—specifically, the same hot spot that currently underlies the Yellowstone area. Because the lava and volcanic ash were carried long distances from their sources, the resulting topography is not dominated by individual volcanic centers or mountains, but rather by a thick, relatively flat surface of volcanic rock that can reach tens to hundreds of meters in depth.231

While the top surface of these flood basalts is typically very flat, the region has since been modified by significant warping, faulting, and the incision of canyons and valleys by rivers.41