Question: What is this Interior Plain called that native Americans such as the Arapaho lived on (other than the Great Plains)?
Sentence (from "East European Plain"): The East European Plain (also called the Russian Plain, predominantly by Russian scientists, or historically the Sarmatic Plain) is a vast interior plain extending east of the North/Central European Plain, and comprising several plateaus stretching roughly from 25 degrees longitude eastward.
Relevant evidence: No