There is a very interesting presentation at Mount Mitchell, the tallest mountain in the Appalachian chain, in North Carolina. When the Appalachians were born, they were larger than the current-day Himalayas and marched right down to the Atlantic. Erosion has slowly worn the Appalachians down to a fraction of their original size and the slow washing of mountains into the ocean has made the coastal area into a bland level plain.   If you want your story to have an interesting U.S. Atlantic coast, just have it take place a few hundred million years ago! If that is not practical, you'll have to move it to the Pacific Coast where plate tectonics and a much younger and more active geology make for a far more interesting coastline.

Bruce