How were the parallel ridges of the Ridge and Valley region formed?

The parallel ridges of the Ridge and Valley region were primarily formed during the Alleghenian orogeny—a major mountain-building event that occurred during the Permian Period, approximately 299 to 251 million years ago.12

This process resulted from the collision of the North American continental margin with North Africa, which exerted immense pressure on the region's sedimentary rock layers. This stress caused a vast "interior crumpling," leading to extensive compressional folding and faulting of the Earth's crust. As the rock masses buckled, they were uplifted into the characteristic parallel ridges seen today. Additionally, thrust faults played a significant role, moving large rock masses over one another, while the subsequent, continuous action of water and erosion further sculpted these ridges and the deep valleys between them.132