Have the great Plains generally expand or shrunk recently and

have the rocky mountains generay expand or shrunk recently

The Great Plains undergo changes from one year to another. These changes are determined by the production of floods, the accumulation of sediments or changes made by man (dams, construction of dams, gravel pits).

The Rocky Mountains shrunk annually. External factors (water, air, wind, freeze-thaw process) cause changes in the structure of the rocks and so there are changes in the mountain landscape.