The Pecos Classification is a chronological division of all known Ancestral Puebloans into periods based on changes in architecture, art, pottery, and cultural remains.
The original classification dates back to consensus reached at a 1927 archæological conference held in Pecos, New Mexico, which was organized by the United States archaeologist Alfred V. Kidder.
Although the original classification has been significantly debated and sometimes modified over the years, the split into Basketmaker and Pueblo period still serves as a basis for discussing the culture of the Ancestral Puebloans of the Four Corners area.
The pre-Ancestral Pueblo culture that moved into the modern-day Southwestern United States after the big game hunters departed are called Archaic.
From evidence near Navajo Mountain, they were nomadic people, hunter-gatherers traveling in small bands.
The original classification postulated a Basketmaker I Period which was subsequently discredited due to lack of physical evidence.
During this period, they began to cultivate gardens of maize (flint corn in particular) and squash, but no beans.
By AD 1050, Chaco Canyon (in present-day New Mexico) was a major regional center, with a population of 1,500–5,000 people.
During the 12th century, populations began to grow after a decline at the end of the Pueblo II Period.
Settlements consist of large pueblos, cliff dwellings, towers and turkey pens.
Socially, this was a period of more conflict than cooperation, which is thought to have led to abandonment of settlements at Mesa Verde.