While North America has more than its share of the world's scenic and spectacular mountain ranges, at the same time it also holds a huge chunk of expansive plains and lowlands. The North America Interior Range2 was created to hold together the enormous chunk of largely non-mountainous terrain between the Rocky Mountains and the Appalachians, and from the Arctic Ocean to the Gulf of Mexico.
Contrary to the belief of many east and west coast mountain snobs, the country between the Rockies and the Appalachians is not "flat". Truly flat land--land with no topography to speak of--is not as common as most people think. You find it on the Atlantic seaboard south from New Jersey; most of Florida; the entire Gulf Coast; and areas in the Mississippi River valley north to Cairo, IL. Some parts of the great plains, such as the Llano Estacado in Texas and New Mexico, also qualify. Anyone familiar with the Delmarva Peninsula, the Everglades, Louisana's bayous, or the Mississippi Delta country knows the real meaning of the term "flatlands".
Most of the rest of North America from the Rockies to the Appalachians can best be called hilly. This includes most of the Midwest, from the High Plains of the Dakotas all the way to Ohio and Kentucky. It's fashionable to deride the Midwest as being flat, but there are plenty of little ski areas, scenic river gorges, and rolling farmland, even in places like Iowa and Kansas. Similarly, the vast Canadian Shield is also covered with uncountable little rocky hills.
While there there are no large ranges of snow-capped or jagged peaks in this huge area, there are certainly plenty of little ranges, highland areas, and hills. The Torngat Mountains of Labrador, the Adirondacks of New York State (which are not Appalachians), the Ozark Highlands of the mid-South, the Black Hills of South Dakota, and the diseccted mesas and badlands of the High Plains are all worthy little pockets of peaks.
Chances are that you have not heard of Fishers Peak, a 9627 feet summit in Colorado that I am calling the highest point of this area. Conventional wisdom gives Harney Peak, the 7242' foot high point of the Black Hills, the title of highest peak east of the Rockies. However, you can make a very logical and persuasive argument that I-25 and Raton Pass are the eastern edge of the Rocky Mountains in the Colorado-New Mexico area. If that is the case, then the extensive highland east of Raton Pass, including Fishers Peak and several other 8000-foot summits that extend east towards Oklahoma, is part of the Interior North America Range2.