Maybe all that game scared them away 1,000 yars ago... Or else they picked the area clean and it couldn't sustain a human population anymore, y'know.
I don't get where people think that the American Indian was such a conservationist society. They killed as much as they could at one time, the easiest way they could do it. Like running entire herds of buffaloes over a cliff when the tribe was hungry and the herds were near, or setting fire to the prairie to drive the game toward the hunters.