Folded mountains have large-scale folding patterns, caused by squeezing and uplifting of stratified rocks. The best way to envision a folded formation is to imagine what happens when you push a carpet on the floor up against a wall. Since it can't move the wall, the carpet begins to fold in a series of bumps that form ridges and valleys. In the same way, folded mountains have straight, parallel valleys and ridges. The valleys are carved out of the softer rocks, while the sturdier rocks form ridges. In Glacier National Park, the mountain building process began around 60 million years ago. Tectonic pressure pushed together, folded, and fractured layers of sedimentary rock. Erosion also helped shape the folded layers. The Appalachian Mountains in the Eastern United States were also formed in this way.