The Teton Range towers over Jackson Hole, where powerful geologic forces began stretching the area less than 10 million years ago and cracked the Earth’s crust to form the 40-mile-long Teton fault. Movement on this fault generates massive earthquakes up to magnitude 7.5, with each earthquake hinging the mountain block skyward and dropping the valley block, leaving no foothills. Ancient granite and gneiss, 2.5 to 2.7 billion years old, form the core of this youthful range. These rocks resist erosion, but over time wind, water, and ice slowly shape the landscape. Glaciers carved and sculpted the dramatic terrain, forming jagged arêtes, U-shaped canyons, and deposited moraines.