The geographical feature forming the western boundary of the Plains Native American cultural region, according to the two maps, is B. the Rocky Mountains.
The Plains covered modern cities and towns like Alberta and Saskatchewan in Canada, Oklahoma City, and Odessa in Texas. It provides the natural environment for food cultivation and cattle ranching.
On the eastern boundary of the Plains Native grasslands is the Mississippi River, giving the large expanse of grassy lands its natural advantage.
Thus, the geographical feature on the western boundary is the Rocky Mountains.
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