The Chaco Phenomenon was an instance of a rapid jump in culture.

Huge three-and four-story houses built with exquisite stonework, and containing hundreds of rooms were built by people that only a short time prior were living in underground pit houses.

During the 11th and 12th centuries the Chacoan people suddenly developed an extraordinary culture, that over generations completed great works of civic architecture.These achievements were only made possible by a social, economic, religious and political system that had not existed before that time. The rapid jump in culture raises perplexing and unanswered questions. Why the marvelous great houses were built and then completely deserted by AD 1250 adds to the mystery of the phenomena.