The Anasazi's Ancestors from 10,000 to 8,000 B.C.

In contrast to the semi-arid conditions that characterize the northern Southwest today, 13,000 years ago the region was relatively moist and green. Paleoenvironmental reconstructions suggest that pine and spruce forests covered much of the area, supported by thick alluvial deposits made by vigorous streams. Mammoth, horse, camel, bison, antelope, and many other large fauna thrived in this context.

This mesic environmental context changed for the worse in 10,000 B.C. For almost 500 years the region apparently experienced a period of desiccation that caused the forests to disappear and grasslands to expand. Even with the return to a moister climate in 9,500 B.C., grasslands continued to dominate the landscape and water levels remained low.

Archaeologists are not certain when humans first entered the Southwest. There are a number of controversial sites vying for the position of the earliest site in the region. The best evidence, however, suggests that a society of hunters and gatherers known as "Clovis people" were the first to settle in the Southwest, probably sometime before 9,500 B.C. They made a distinctive lanceolate point with shallow fluting and also crafted mammoth bone and ivory into a variety of useful tools. Clovis people hunted a variety of animals, from mammoth to bear to jackrabbit. Large fauna such as mammoth were often hunted using a method known as "catastrophic cropping" in which an entire matriarchal herd would be killed. In other cases, only single kills would be made and Clovis are even suspected to have scavenged carcasses left by other predators.

Clovis sites are fairly ephemeral, with most of those discovered representing areas where game was killed and processed. One site, Ventana Cave, may have served as a base camp for a small band consisting of a few families. Dating to 9,300 B.C., this rockshelter includes grinding stones, indicating that plant resources played an important role in Clovis diet. Artifacts recovered from sites such as Ventana indicate that Clovis people were obtaining high quality lithic materials from as far away as 300 km. This suggests that bands were either highly mobile or they participated in spatially extensive exchange networks.

By 8,800 B.C., the Clovis culture seems to have disappeared as people changed their behaviors and new traditions emerged. This is correlated with the extinction of the mammoth in the Southwest, an event that some scholars believe was caused by a combination of human overhunting and a period of environmental desiccation beginning around 9,000 B.C. These changes are correlated with the emergence of several new cultural traditions in the Southwest, including the San Dieguito in the extreme southwestern United States and the Plainview and Agate Basin traditions in what is now the Plains.

Two of these new traditions provide the historical context for the emergence of the Anasazi: the Folsom Complex and the Cody Complex. The relatively well-known Folsom Complex, located in the eastern and central areas of the Southwest, is represented by a fully fluted and beautifully made style of projectile point. Like the preceding Clovis people, most Folsom sites are kill and processing sites associated with hunting a now extinct species of bison, antelope, canids, and rabbits. The materials recovered from Folsom kill sites suggest that bison were by culling single animals from the herd. Archaeologists believe that Folsom people tended to follow the same few herds over a large area. This high mobility may explain the development of highly efficient methods for making stone tools, which allowed mobile bands of people to minimize the quantities of raw materials they had to carry with them.

The Cody Complex exhibited many similarities to the Folsom people. However, there is evidence that Cody people also utilized massive bison kill sites in which entire herds of animals were killed. A classic example is the Olsen-Chubbock site in Colorado, where a large herd was driven over a cliff. Not only does this hunting technique require a lot of labor, but it also produces literally tons of meat, suggesting that at times large numbers of Cody people gathered to participate in these massive kills.