The Anasazi built 14 multistory sandstone "great houses" between A.D. 850 and 1150 in Chaco Canyon. The structures averaged more than 200 rooms apiece and were up to four stories tall. The largest and best-known site, Pueblo Bonito, held 700 rooms. The purpose of the Chaco great houses has been debated for more than a century, one idea being that they were the sites of ritual feasts that pilgrims traveled from afar to attend. During those events, Chaco Canyon's population may have swelled to 7,000 or more - so how did the Chacoans feed all those hungry mouths?

Paltry precipitation, a short growing season and unreliable flows in the Chaco Wash made canyon corn production precarious. Even so, until the 1970s most archaeologists believed the Chacoans grew all their crops there. That idea was supported by the findings of R. Gwinn Vivian, an Arizona archaeologist who uncovered an extensive system of dams, canals, ditches and walls used to channel Chaco runoff to farming terraces, garden plots and fields.

But in the 1970s, aerial photography and satellite images began to reveal the extent of the prehistoric road network that links Chaco Canyon to outlying communities across the San Juan Basin and beyond. More than 400 miles of ancient roadways have been identified. They tie the core area around Pueblo Bonito to more than 150 other great houses in a region the size of West Virginia. It became clear that the Chaco Canyon great houses were once the hub of the San Juan Basin. The roads were spokes connecting that hub to the outlying communities.

More recently studies have shown that the Anasazi used the roads to haul roof timbers to Chaco - without the help of draft animals or the wheel - from the base of the Chuska Mountains, 50 miles to the west. Clay pots and chert, a fine-grained rock used to make projectile points, also were imported from the area. It is now being wondered if the same was done with corn.

Three years ago a team of corn project researchers began an on-going investigation to collect new soil samples in and around Chaco Canyon, looking for likely Anasazi farming sites. The chemical content of seven prehistoric corn cobs collected at Pueblo Bonito by archaeologist George Pepper between 1886 and 1899 have been analysed, along with soil and water samples from likely agricultural sites in and around Chaco Canyon. The strontium ratios in the Pueblo Bonito cobs matched soils from the base of the Chuskas and from the San Juan and Animas river flood plains 56 miles to the north, suggesting the corn had been imported from theat area.

That result is overturning the long-held belief that the Chacoans were agriculturally self-sufficient, growing everything they needed within the canyon through the clever use of captured and diverted surface runoff. It now appears that during its heyday in the mid-1000s, Chaco Canyon was as dependent on outside supplies as an Antarctic base. It was sustained by shipments of timber, pottery, stone and food carried in from the edges of the San Juan Basin. It also took in trade goods from Mexico, including copper bells, macaws and seashells from the Gulf of California.

The findings also reinforce the view that Chaco was the ceremonial, administrative and economic center of a vast region spanning northwestern New Mexico's San Juan Basin in the 1000s. Surplus corn was brought to the central hub from fields on the edges of the basin, then redistributed to struggling farmers in other areas.

The building boom in Chaco Canyon ended in the mid-1100s and the region's population center shifted northward. By 1300, Chaco Canyon and most of the northern Southwest had been abandoned by the Anasazi. Drought may have contributed to the abandonments.

[information gleaned from a news article in the Rocky Mountain news]