The correct answer is: The Rocky Mountains.
Plains Native Americans lived in a combination of <em>sedentary settings and nomadic lifestyle. </em>They planted crops and established villages in the spring, they focused on hunting in the summer and winter and harvested their crops in the fall. Plains Native Americans used <em>two primary methods</em> for establishing boundaries,<em> warfare and geography</em>.
Usually natural land formations or rivers served as a marker of tribal territory. The Great Plains lie between<em> Rio Grande</em> in the south,<em> Mackenzie River</em> in the north, between the <em>Interior Lowland</em> and the <em>Canadian Shield</em> on the east, and the<em> </em><em>Rocky Mountains</em> on the west. (The Rocky Mountains served as a barrier and the Indian Americans ruled the land).
The Rocky Mountains range over 3,000 mi from British Columbia to New Mexico and reach a height of 14,440 ft.