Pueblo Bonito beneath the Cretaceous Cliffhouse Sandstone

Pueblo Bonito is the largest of 14 pueblo great houses built by the Anasazi in Chaco Canyon between 900 and 1150 CE. The D-shaped floor plan included several stories, 800 rooms, and a central plaza with 32 ceremonial kivas. Archeologists and anthropologists agree that Chaco was the focus of Anasazi life in the San Juan Basin, although the nature of the relationship is debated. The influence is inferred from architectural and pottery similarities and a network of ancient roads to outliers like Salmon Ruin and Aztec Ruins near Farmington, New Mexico.

Why Here?

At first glance, the area around Chaco Canyon seems fairly desolate, not at all the sort of place you'd expect a community of 5000 to live and thrive. But the climate was a little wetter 1000 years ago and the canyon receives storm runoff from a significant area. With creative planning and labor intensive irrigation techniques there was enough food to support a growing population.

Why Did They Leave?

A 50-year drought began in 1130 and coincided with a downward turn in Chaco activities. What would you do if food started getting scarce? As your stores were depleted you'd have to work harder to bring in crops under drought conditions. You'd stop building new houses and may not worry as much about where you threw your trash (both of which happened). As the drought continued you'd start to wonder if you'd be better off leaving and finding a better home. Finally, you would pack up your family and essentials and move on. There is no evidence at Chaco of violence or sudden abandonment. People just bit by bit packed up and left. By 1300 Chaco was deserted.

1898 Pueblo Bonito was first excavated between 1896 and 1899. This photograph was taken by George H. Pepper from the north mesa overlooking the great house. Chaco Wash is the dark line between the ruins and the far mesa.

1935 In 1941, part of the canyon wall we're standing on broke away from the mesa to the left of this photo. A section of the ruin rear wall and some rooms were destroyed.

1986 This view has been widened to the left to show the entire ruin and the 1941 rockfall.

Recent Research
		Tree rings are useful for more than dating. They can also help identify timber source areas, a method called tree-ring sourcing. Recent work indicates that most wood came from the Zuni Mountains before 1020 CE and the Chuska Mountains afterwars. So how did Chaco builders drag 5-m beams 75 km without pack animals and and hardly scratch the wood. And once there, how did they lift the heavy beams up to a six-story height? Diamond, Jared (2016), Archaeology: Sources of Chaco wood. Nature 529, 31-33. http://dx.doi.org/10.1038/nature16864 Guiterman, C. H., Swetnam, T. W. & Dean, J. S. (2015), Eleventh-century shift in timber procurement areas for the great houses of Chaco Canyon. Proc. Natl Acad. Sci. http://dx.doi.org/10.1073/pnas.1514272112