How did lava flows help form the Columbia Plateau?

The Columbia Plateau was formed through extensive volcanic activity that occurred between approximately 17 and 14 million years ago. During this period, a massive flood of mantle-derived basaltic lava and volcanic ash buried the preexisting terrain.123

These lava flows, often referred to as flood basalts or traps, were typically erupted from long fissures rather than single volcanic centers. Because the lava was highly fluid, it was able to travel long distances, creating thick layers of volcanic rock that reached tens to hundreds of meters in depth. This process effectively leveled the landscape, resulting in the characteristic flat surface of the plateau. While the top surface of these flood basalts is generally very flat, the region has since been shaped by subsequent warping, faulting, and the erosion of sharply incised canyons and valleys by rivers such as the Columbia and Snake.345