About two hundred million years ago, the landforms drifted into their current configuration as continents.

Sixty-five million years ago dinosaurs became extinct. Twenty to fifty million years ago, volcanoes spewed molten lava and tectonic shifts helped form mountainous areas in the Northwest.

Seventeen million years ago, some scientists believe a giant meteorite struck southeastern Oregon, causing floods of basalt lava. For a period of approximately four million years, lava spilled across the western lowlands and the Columbia Plateau began to form one of the largest basalt Plateau’s in the world. Indeed, 42,000 cubic miles of lava flooded the Northwest from present day Lake Roosevelt into Oregon. In some places, the basalt is more than two miles thick.

Lake Roosevelt sits on the northern edge of these flows. The lava filled valleys, turning eastern Washington from a land of hills and mountains into a great, flat plateau. Today, there are many places where layers of lava can still be seen.

About one million years ago, these volcanic fires were followed by the deep freeze of the ice age.