Subsequent Erosion
The mountains formed by the Alleghanian orogeny were once rugged and high, but in our time are now eroded into only a small remnant: the heavily-eroded hills of the Piedmont. Sediments that were carried eastward formed the coastal plain and part of the continental shelf. Thus, the coastal plain and Piedmont are largely the byproducts of erosion that took place from 150+ million years ago to the present.
Sediments that were carried westward formed the Allegheny and Cumberland Plateau, which in some areas are popularly called mountains, but are actually simply uplifted and eroded plateaus. Carbonates and fine sediments from the Alleghanian orogeny were carried farther west to form limestone rocks in a shallow sea that was later uplifted and forms the bulk of Tennessee, Kentucky, Ohio, and Indiana.
A portion of the Alleghanian mountain system departed with Africa when Pangaea broke up and the Atlantic Ocean began to form. Today, this forms the Anti-Atlas mountains of Morocco. The Anti-Atlas have been geologically uplifted in relatively recent times, and are today much more rugged than their Alleghanian relatives.
Read more about this topic: Alleghanian Orogeny
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