Fallen City Interpretive Site sits along the Bighorn Scenic Byway. Fallen City In the process of uplift which created the Bighorn Mountains, faults and fractures formed in the rocks. The thick layers of limestone in this area were fractured parallel to the valley. When a section of the Earth’s crust sank, huge chunks broke loose from a layer of rock, resulting in the massive boulder field before you. Because of the geometric shapes of the rocks, the boulders can be imagined as the toppled buildings of a “fallen city.”