Any time I hear the word "plateau", I usually associate it with the tallest in the world, Tibet. Anyone who looks closely at a map will see that the southern line of the plateau parallels the location and length of the Himalayas, leading to the assumption that the collision between India and mainland Asia, which resulted in the formation of the Himalayas, also forced Tibet upwards, creating the highest great plain on Earth.
The Altiplano is classified as a plateau, yet it does not span the entire length of the entire Andes, the longest mountain range in the world. Nor does the Colorado parallel the whole length of the Rockies.
So if a plateau is not formed as originally lowlands forced upwards by nearby mountain-building, then how does it REALLY form?