It's not quite accurate to talk about "capitals of interior plains" because the Interior Plains are a geographical region, not a political entity. They span several countries and encompass many states and provinces.

To answer your question more accurately, let's break it down:

* The North American Interior Plains: This region includes parts of Canada, the United States, and Mexico. Some of the major cities within this region that could be considered capitals (either of states/provinces or significant economic/cultural hubs) include:

* Canada: Winnipeg (Manitoba), Regina (Saskatchewan), Edmonton (Alberta), Saskatoon (Saskatchewan), Calgary (Alberta)

* United States: Denver (Colorado), Oklahoma City (Oklahoma), Lincoln (Nebraska), Des Moines (Iowa), Bismarck (North Dakota), Pierre (South Dakota), Cheyenne (Wyoming), Santa Fe (New Mexico).

* Mexico: Monterrey (Nuevo León)

* Other Interior Plains around the world: There are other interior plains in places like South America (the Gran Chaco), Asia (the Eurasian Steppe), and Australia. You would need to specify the specific region to identify the relevant capitals.

Let me know if you have any other questions!