From Ϸ11,200 to 8,000 years ago, the Great Plains of North America were populated by small Paleoindian hunting groups with well developed weaponry and the expertise to successfully hunt large mammals, especially mammoths and bison. Mammoths became extinct on the Plains by 11,000 years ago, and, although paleoecological conditions were worsening, their demise may have been hastened by human predation. After this, the main target of the Plains Paleoindian hunters consisted of subspecies of bison, Bison antiquus and Bison occidentalis. As bison populations gradually diminished, apparently because of worsening ecological conditions, by Ϸ8,000 years ago, human subsistence was forced into a greater dependence on small animal and plant foods. Human paleoecology studies of the Paleoindian time period rely heavily on multidisciplinary efforts. Geomorphologists, botanists, soil scientists, palynologists, biologists, and other specialists aid archaeologists in data recovery and analysis, although, with few exceptions, their contributions are derived from the fringes rather than the mainstream of their disciplines.The time and circumstances surrounding the arrival of the first human inhabitants of North and South America has become a lively topic for debate (1, 2). However, the Northern Plains and montane basins of the central and southern Rocky Mountains have produced some of the best preserved evidence of North America's earliest known pedestrian, large mammal hunters whose presence is documented during the closing years of the Pleistocene after Ϸ11,500 years ago. Other groups, recognized by weaponry and tool assemblages, were present until Ϸ9,000 years ago. By 11,000 years ago, a number of large mammal species, including the mammoth, mastodon, camel, and horse were extinct or nearly so, and the older subspecies of bison would follow soon after. The search for an explanation of these Pleistocene extinctions has been another lively and controversial topic for paleontologists, biologists, geologists, and numerous other specialists for several decades (3, 4). The debate turns on whether the late Pleistocene extinctions were the results of paleoecological changes, human predation, or a mixture of both. The problem shows no signs of an immediate resolution (5-7).The confirmation in the 1920s of human presence with an extinct subspecies of bison at the Folsom site in northern New Mexico (8) and the mammoth at the Dent site in Colorado (9) as well as the Blackwater Draw site in eastern New Mexico shortly afterward (10, 11) drew archaeologists into the subject of Pleistocene extinctions. However, they addressed problems differently from most specialists of the Pleistocene and focused mainly on human predator-prey relationships. These included the time of year, location, and geologic features utilized in animal procurement events; butchering and processing; and the amount and distribution of food products, all of which could assist the archaeologist in determining the social and subsistence activities of the human groups i...