Read this: Cultural practices in the Americas seem to have been shared mostly within geographical zones where unrelated peoples adopted similar technologies and social organizations. An example of such a cultural area is Mesoamerica, where millennia of coexistence and shared development among the peoples of the region produced a fairly homogeneous culture with complex agricultural and social patterns. Another well-known example is the North American plains where until the 19th century several peoples shared the traits of nomadic hunter-gatherers based primarily on buffalo hunting.

How long was there a homogeneous culture on the North American plains?
What is the answer? (If it cannot be answered, return "unanswerable")
until the 19th century