Re “There are few major cities in the U.S. great plains. Where they do exist, it’s either along the rivers that serve as shipping lanes and electricity providers, or at the mountains below major passes and interstates.”
If you use the Census Bureau’s definition of the counties that make up the Great Plains, there are only two major cities: Denver and Austin. Both sit at the extreme edges of the Plains, neither of them is historically Plains-oriented , and neither satisfies the description you give. There are no navigable rivers across the Plains. The Missouri River dams produce significant electricity, but haven’t produced cities of any size. Neither Denver nor Austin sit on a major east-west Interstate, and neither was on a route for a transcontinental railroad. The I-70 extension west from Denver was an afterthought added after Colorado called in every political favor it could, and based on traffic, is primarily a connection between Denver and the mountain resorts on the west side of the Divide.
 Austin’s historical economic focus was always to the east, away from the Plains, and Denver’s to the west, into the mountains.