The Ozark Plateaus and Ouachita Mountains cover the northwest half of Arkansas. These highlands are related to the Appalachian Mountains. The Ozark Plateaus are often called mountains. Yet plateaus are supposed to be flat. Not at all.
Plateaus are flat lands that have been elevated.
After they are raised, rivers and streams may create valleys. As the valleys become larger, the ridges they separate come to resemble mountains. The Ozarks are plateaus that have been carved into mountains. The mountains, by the way, have flattish tops. The rugged, forested Ozarks are famed for their scenic beauty and underground rivers carrying dissolved minerals.