Final answer:
The Navajo Nation is the largest Native American Reservation in New Mexico and the U.S., located in the Southwest region.
Step-by-step explanation:
The largest Native American Reservation in New Mexico and the entire United States is the Navajo Nation. This reservation spans a vast area and is situated in a natural province or region known as the Southwest, encompassing parts of New Mexico, Arizona, and Utah.
The Navajo Nation is an autonomous jurisdiction with over 325,000 members, and it is known for its rich cultural heritage, including traditional weaving and matrilineal society structure.