What topographical changes have taken place in North America in the past few hundred million years?

Answer 1

Check out these paleogeographic reconstructions by Dr. Ron Blakey of Northern Arizona University: http://jan.ucc.nau.edu/~rcb7/global_history.html
Start with Jurassic link, and move up the time scale to Cretaceous, Eocene, Miocene, Present.
These will take you to maps showing the break up of Pangea and the creation of the eastern coastlines associated with the formation of the Atlantic and Gulf of Mexico --and will illustrate a long history of various episodes of mountain building on the west coast (Nevadan, Sevier, Laramide orogenies).
You can see locations of incursions of inland seas in times such as the Cretaceous.