The Great Houses
The Chacoans cut an estimated 225,000 trees, hauled from mountain forests sixty miles away, to build the great houses and kivas of Chaco Canyon. These log beams supported the roofs of the great kivas and the floors in the rooms of the great houses. They also helped to establish when the great houses and kivas were built.
The technique is called tree-ring dating, or "dendrochronology." Varying climatic conditions—heavy rains, droughts, temperature shifts—create a distinct pattern in the annual growth rings of all of the trees living in a geographical area.
and correlating these patterns allows archeologists to fix the date
that trees were cut, sometimes down to the year or even the season.
For example, tree-ring dating reveals that Pueblo Bonito was built
in several stages that spanned three hundred years.
Early construction was done using simple walls one stone thick. Later, multistory great houses were built with a rubble core capped with a veneer of thin sandstone slabs, sometimes in mosaic-like patterns. The latest masonry style found at Chaco Canyon is a thin inner core of rubble surrounded by a thick, blocky veneer.