Final answer:
The northeastern region of the United States is characterized by diverse landforms, including the ancient Appalachian Mountains, and various plains such as the Interior Lowlands and the Great Plains, as well as the Canadian Shield and the Atlantic Coastal Plain.
Step-by-step explanation:
The northeastern region of the United States features a diverse array of physical environments and landforms. One prominent landform found in this region is the ancient Appalachian Highlands, which is a significant mountain range extending through many states including the northeastern ones. While less rugged than the Rocky Mountains, the Appalachian Mountains have played an important role in the history and development of the United States. The region also includes plains like the Interior Lowlands and the Great Plains.
To the north of the Appalachians is the Canadian Shield, which is geologically the oldest part of North America, characterized by sparsely populated areas with poor soils. At the southern and eastern edge of the continent, there is the Atlantic Coastal Plain. Additionally, in northern New England and the Canadian Maritimes, the terrain becomes more rugged and the soil less fertile.