The Teton Range and the valley before it formed like two parts of a giant hinge as the Earth’s crust stretched and broke into two blocks along the forty-mile-long Teton fault. Fractures along the fault generate large earthquakes. The western block hinged up and became the Teton Range, while the eastern block tilted down and formed the valley. As the mountains rise, wind, water, and ice wear down the jagged skyline and erode away sandstone and limestone layers except for small outcrops. The landscape continues to change, and geoscientists predict future earthquakes up to a 7.5 magnitude. The Teton Range is made of some of the oldest rocks on Earth, yet it is one of the youngest mountain ranges in North America. The stretching, cracking, and tilting that formed the Tetons began only nine million years ago, while geologic forces thrust up the Rockies more than seventy million years ago.