Why do some anthropologists group the Plateau and Great Basin as the Intermontane culture area?

Anthropologists sometimes group the Plateau and Great Basin regions into a single Intermontane culture area because the southern boundary of the Plateau ecosystem gradually merges with the northern reaches of the Great Basin, making the boundaries between these two culture areas imprecise.1

The use of the culture area approach is a typology in anthropology used to organize and compare cultures based on geographic regions where certain traits generally co-occur. Because the specific number of delineated culture areas can be variable, scholars occasionally choose to conjoin regions that share geographic or cultural similarities. In this case, the transition between the basin and range systems of the Great Basin and the high intermontane plateaus of the north provides a logical basis for considering them as a joint, larger cultural unit.213