Whoa! You just moved my hometown, Chicago, about 1,000 miles.
Which regions are you considering? What are their names?
The physical regions, like Prairies, interior, plateau, rockies, coast mountain, tundra, plains, Can. Shield. etc.
Which regions are you using for the United States? Obviously we do not have the Canadian Shield. But we have other regions that you haven't mentioned. And what about the Great Lakes and Northeastern regions?
What regions does your book use for the U.S.?
What city in the US would I find laying in the Great Plains and the Rockt mountains?
Denver, Colorado is on the edge between the Great Plains and the Rockies.