Timber & Snowmelt, Pueblo Bonito

Meltwater from an April snow deepens the color of stone work
surrounding a timber in Pueblo Bonito. Rings in the timber are
readily visible. Together with a lifetime of other examples,
tree-rings like these allowed astronomer A. E. Douglas to found
the science of dendrochronology which precisely dates -- to the
year and to the season -- the construction of buildings throughout
the Southwest. Next, isotopic analysis may allow these and other
timbers to be traced to the precise hillsides from which they were
cut. In Chaco Canyon's case, the nearest candidate groves are tens
of miles away.