One of Earth’s longest ancient fault lines stretches nearly 1,000 miles, from Flathead Lake, Montana, almost to the northern border of British Columbia in Canada. “The Rocky Mountain Trench gives us a picture of a historical event that started over 100 million years ago,” says Charles Trautwein. The first part of the action was the sliding of the Pacific tectonic plate. As it moved under the North American plate, it ruptured the overlying rocks. Over several ice ages, explains Trautwein, the repeated advance and retreat of glaciers scoured out canyons, scraping away structurally weakened rocks and forming the impressive Rocky Mountain Trench.
Linda Shiner is the editor of Air & Space.