The steep fault scarp near the base of Mount St. John formed as several massive earthquakes broke the ground by more than 75 feet since ice-aged glaciers last retreated 14,000 years ago. The Teton fault began moving roughly nine million years ago, generating earthquakes that shook the landscape. In earthquakes as large as magnitude 7.5, the mountain block was lifted one part for every three to four parts that the valley block dropped, building the range one step at a time. Future earthquakes will continue to shape this landscape, though geoscientists cannot predict when. An earthquake occurs when two blocks of the Earth’s crust slip past one another along a crack called a fault. During larger earthquakes, the fault breaks the Earth’s surface and forms a vertical escarpment or scarp, providing lasting evidence that an earthquake occurred. Over time, erosion degrades the scarp and leaves behind a gentler slope.