Being Native Amercan myself, I have long been fascinated with Chaco Canyon, its system of roads and great pueblos. I could yak about Chaco Canyon for days, so, I'll to be brief in presenting some main ideas. I think Chaco Canyon was some sort of trading center. The largest pueblo resembles a warehouse of storerooms and auction or trading floors. Native Americans from as far away as the Canadian plains, the Great Lakes and Mexico may have made pilgrimages to Chaco to trade primarily seeds and ideas. How did corn spread from the Amazon to the Great Lakes? Up here in Canada, though rare, we find the occasional pre-columbian artifact of silver or copper that seems to have come from central american metal working peoples. They probably traded furs from the north for the metal artifacts. We do not find furs or much other organic material at Chaco Canyon though. I think Chaco Canyon was abandoned because of some kind of mircobial plague. The storerooms were cleaned out spotlessly as an attempt at dealing with the fungi or whatever it was. Eventually the large wooden roof beams were burned as a final attempt at purging the microbe. When all failed they simply had to abandon the now useless trading center and never found conditions suitable elsewhere to rebuild before the arrival of Europeans. The layout of the roads and local geography seem to make it easy for pilgrims from distant regions to find the trading center from hearsay, sketchy or handed down descriptions of its location. Using the night sky as a reference this layout may also have provided a crude mental map making it easier for pilgrims leaving the region to find their way back again or tell someone else how to find the trading center. The thin soils in the region of Chaco Canyon seem unlikely to have been able to provide the calories needed to do all the building in the region by human muscle power. In medieval Europe it took the thick rich soils of a entire small country to supply the calories needed to build a stone cathedral similiar to the great pueblos. Food must have been imported from eslewhere in large quantities to build Chaco Canyon. Likely the calories mostly came from the south in the more fertile regions of Mexico. What was so valuable at Chaco Canyon to make this trade worthwhile? Trade in seeds and ideas (technology)!