Past Walla Walla, Washington, we drop down into the Columbia River Gorge. Between about 17.5 and 6 million years ago massive eruptions of flood basalts engulfed about 63,000 square miles (164,000 km2) of the Pacific Northwest, ultimately accumulating to a thickness of more than 6,000 feet (1.8 km).
All images copyright © 2016 F.W. Vollmer and may not be used without permission.