Chaco Canyon between A.D. 800 and 1250. Skilled builders and traders, they developed advanced irrigation systems and lived in massive, sophisticated pueblos. One multistoried complex contained some 800 rooms. Between 30 and 40 Anasazi towns were linked hundreds of miles of smooth dirt roads, some 30 feet wide. The roads also led to agricultural areas and rock quarries, indicating a highly organized network of farming, man- ufacturing, and commerce.
The calendar is as accurate as any known mechanism...