Only the northernmost portions of the Coastal Plain were affected by Ice Age glaciers. These include Cape Cod, Massachusetts, and Long Island, New York. The Coastal Plain disappears in northern New England. It has not been destroyed, but is simply underwater. On the Pacific Coast, the continental shelf is much narrower, and geologists don't even talk of a coastal plain.
High cliffs tower over the edge of the sea in some places.
That's because this area is so active geologically. Volcanoes and earthquakes mark this region where the ocean basin plunges underneath the North American continent. A great resource to use with the article below is the U.S. Geological Survey's new Tapestry project, beginning with the maps below. The numbers by the regions in the table below correspond with the numbers in the Physiographic Map. For example, number 3c on the map illustrates the Floridian section of the Atlantic Coastal Plain.