What is the antonym of Piedmont?

The term "Piedmont" refers to a geographical region characterized by its foothills, typically at the base of mountains. An antonym for Piedmont could be "highland" or "mountain," as these terms denote elevated areas rather than the lower, sloping regions that characterize a Piedmont. Another possible antonym could be "plain," which describes flat, low-lying areas without the foothill features associated with Piedmonts.