The wood in the monumental "great houses" built in Chaco Canyon by ancient Puebloans came from two different mountain ranges, according to new research from the University of Arizona Laboratory of Tree-Ring Research.
The UA scientists are the first to report that before 1020, most of the wood came from the Zuni Mountains about 50 miles (75 km) to the south. The species of tree used in the buildings did not grow nearby, so the trees must have been transported from distant mountain ranges.
About 240,000 trees were used to build massive structures, some five stories high and with hundreds of rooms, in New Mexico's arid, rocky Chaco Canyon during the time period 850 to 1140. The buildings include some of the largest pre-Columbian buildings in North America.
"The casual observer will see hundreds and hundreds and hundreds of beams sticking out of the walls. There's wood all over the place in these structures," said lead author Christopher Guiterman. "They're built out of stone and wood."
To figure out where the trees for the beams had grown, Guiterman used a method known as dendroprovenance that had not been used in the American Southwest before.
By 1060, the Chacoans had switched to harvesting trees from the Chuska Mountains about 50 miles (75 km) to the west.
The switch in wood sources coincides with several important developments in Chacoan culture, said Guiterman, a doctoral candidate in UA's School of Natural Resources and the Environment.
"There's a change in the masonry style--the architectural signature of the construction. There's a massive increase in the amount of construction--about half of 'downtown Chaco' houses were built at the time the wood started coming from the Chuska Mountains," he said.
By reviewing archaeological records, the team found other materials coming to Chaco from the Chuskas at the same time.