How did folding and faulting create mountain ranges in the Middle Rockies?

In the Middle Rockies, mountain building occurred primarily during the Laramide Orogeny (approximately 70 to 40 million years ago) through a combination of compressional folding and high-angle faulting.12

Unlike the Canadian and Northern Rockies, which are characterized by extensive low-angle thrust-faulting, the Middle Rockies were shaped by the uplift of large crustal blocks. This process involved the following mechanisms:13

• Compressional Folding: The region experienced compressional forces that arched sedimentary rock layers upward, creating anticlinal mountains.1
• High-Angle Faulting: These compressional forces caused the granitic basement rock to be upfaulted, pushing blocks of Precambrian rock toward the surface. These exposed crystalline cores now form the centers of many ranges, such as the Wind River Range and the Uinta Mountains.12
• Exceptions: While most of the region was shaped by these processes, southwestern Wyoming and southeastern Idaho experienced low-angle thrust-faulting similar to the Northern Rockies, and the Teton Range attained its height more recently through movement along an east-dipping fault.1

These tectonic events created the characteristic sharp ridge lines of the Middle Rockies that rise prominently above surrounding basins.1