If you can grow wheat there, it's the prairie. Therefore the Midwest. Just how the eastern parts of Colorado are the furthest west parts of the mid west. Unless you want to exclude the prairie states entirely from the mid west, which i wouldn't do.

I can say for sure none of it's very Northwestern; even eastern Washington is more like Idaho than the coast.

Rockies is fair, for the part that they actually run through, which seems to be more like a third of the area and inevitably less populated. I guess that's the part they like to advertise, though, and clearly it has worked.