Final answer:
The Ridge and Valley region of the eastern United States was mainly formed as a result of tectonic uplift caused by the Taconic and Acadian Orogenies.
Step-by-step explanation:
The Ridge and Valley region of the eastern United States was mainly formed as a result of tectonic uplift caused by the Taconic and Acadian Orogenies. These orogenies were mountain-building events that led to the folding and faulting of the Earth's crust, resulting in the formation of long ridges and parallel valleys in the area. While erosion plays a role in shaping the Earth's surface, it is not the main process responsible for the formation of the Ridge and Valley region.