In the mid-13th century, Native American corn growers and their families fled their drought stricken farms south and west of their cultural center at Chaco in what is now New Mexico.
Image Credit: National Park Service: Pueblo Bonito, Chaco National Park
These ancestral pueblo peoples had endured year after year of drought. The religion and agronomy promoted by the Chaco elite had failed to induce the rain gods to nurture their crops. Famine destroyed their faith and led them to seek territory with more rain. Some fled north to the higher altitudes of southwestern Colorado and southern Utah. They built many pueblos on the mesas drained by McElmo’s Creek and farmed the mesa tops and stream bottoms. Canyons of the Ancients.
The crops thrived with more rain, but at the higher altitudes, the growing season was shorter and variable. A late planting or an early frost severely cut into the yields of corn, beans, and squash. Moreover, they competed for arable land with peoples who had been farming in the region for centuries.
Facing starvation, the men of a stricken pueblo would attack a town that had more ample food. The warfare destroyed vulnerable pueblos and led others to settle in defensible sites. For example, the Hovenweep settlement.
Perhaps, most dramatically, were the many defensive pueblos built below the southern rim of Mesa Verde.
Ancestral pueblo peoples had lived on top of the mesa for about three centuries. The arrival of immigrants from the south along with drought led to conflict. For safety, they built the spectacular pueblos below the mesa top that are now preserved at Mesa Verde National Park.
However, the drought and the social chaos it generated forced the peoples to abandon the metro-complex that they had built at Mesa Verde and the Canyon lands. Most of them re-settled in the upper Rio Grande Valley and developed the various Pueblo societies and cultures that now reside there. Link