Decline of Hohokam


The remnants of the Great House at Casa Grande

For reasons that are subject to debate, during the period of 1400 to 1500 A.D. large community centers  of the Hohokam were abandoned, as were many canals. The people did not die out, they moved instead to smaller villages. They adapted to some changed conditions in other words. What really interests me is why this occurred. It is one of the genuine mysteries of North American archaeology. I believe it has continuing important significance for our modern societies. There are lessons for us to learn here. Will we learn them?

When Spanish missionaries arrived at the end of the 17thcentury they found only an empty shell of the once flourishing village of Casa Grande (as the Spanish called it). Over the next two centuries, many visitors visited the site and damaged it over and over again.  In the late 1800s scientists pressed for its formal protection and in 1892 Casa Grande Ruins National Monument became America’s first archaeological reserve. To this day, the Great House keeps the secrets of the Ancestral People of the Sonoran Desert within its protected walls.

At one time 2,000 people lived in Casa Grande and it had the most extensive canal system in North America, if not the world. It required an amazing amount of human labor and engineering to create the Great House, the remnants of which we saw in the park.

The main building material was caliche (cu-LEE-chee), a concrete like mixture of sand, clay, and calcium carbonate (limestone). It took 3,000 tons of caliche to build the Great House.

Caliche mud (water was added to the caliche) was layered to form walls that were about 4 ft. thick at the base, tapering toward the top. Hundreds of juniper, and fir trees were carried or floated down the Gila River to the village. Timbers were anchored in the wall for ceiling and floor supports.

Caliche is found as hard pan in most areas at depths of 6 inches to 2 feet. It is hard like concrete. I often saw it on my hikes in San Tan Mountain Regional Park, about 10minutes from where we lived for the winter.  It can be softened in water, however, and that is why the ancestral people created mud with the addition of water to the caliche. That was stacked on to the buildings and then allowed to dry to a very hard material.

How civilized were the Hohokam? There is no evidence that the ancestral people invented the wheel. Since they had no draft animals, and since usually the rivers did not flow to their agricultural lands, they had to carry all of their building materials.

Since 3,000 tons (6 million pounds) of materials were needed for the construction of the Great House, that meant that 100,000 bags each with about 60 pounds of mud had to be carried up to the Great House.

The Great House consisted of a 4-storey structure on a mound of about 4 feet. The mound was used for the same reason that judges sit on a high bench and preachers stand above the congregation at their pulpit. It is a sign of prestige to be high up. The Administrators of the region likely wanted to be seen to possess authority. The first floor of the Great House consisted of a mound or platform. It was there solely for purposes of building it up so it looked more impressive.

The second floor contained 5 rooms as did the 3rdfloor. The 4thfloor consisted of just one room.  As a result timbers from the mountain trees had to be brought in by hand. It is likely that the ancestral people subcontracted the job by trading for such materials. 640 logs were needed for the Great House construction. The timbers came from about 50-75 miles away. Arduous hauling was needed to get them to the site.

The roof was made by spreading saguaro ribs across the beams with reeds covering them, and then topped with a final layer of caliche mud. Despite centuries of weathering and neglect the Great House remnants still stand testifying to the nature of the society of Ancestral People. In recent years the canopy was built to protect the Great House. The doors of the Great House were quite small, not because the people were so small, but to keep out warm air.

Like so many Indigenous peoples of the Americas, the Hohokam were careful to align their structures with celestial bodies. They did that, I think, to connect to the large world “out there.” The Great House at Case Grande was carefully aligned with the sun. But that was not all. In fact 17 different astronomical observations could be made from the house.  First of all, the house was carefully aligned between North and South.

There was also a round hole “window” that once each year lined up perfectly with the sun on the day of the summer solstice. Another rectangular hole carefully marked the spring and fall equinoxes. As well one square window lined up with the Lunar Standstill that occurred every 18.6 years. No one is sure exactly why these alignments were produced, but they do show the sophisticated knowledge of astronomy that the Ancestral People had.

These odd alignments are all part of the mystery about the purpose behind the Great House.  It took an astonishing amount of human labor to create the house, but it was abandoned within about 75 years, even though the Ancestral People inhabited the area for more than 1,000 years. According to Rose Houk,

“Modern archeologists have observed such an alignment of the sun through a “window” in an upper room of Casa Grande, marking the summer solstice. They have suggested that the “great house” may have been used as an astronomical observatory, one of several ideas about this enigmatic, imposing structure that stands out in the desert of central Arizona. Others have seen the four-story building as a fort, a granary, or a silo.  Whatever the truth, the Casa Grande’s significance was recognized early on when it became the nation’s first archaeological preserve in 1892.”

A steel and concrete canopy was built in 1932 to protect the Great House from the elements.

As I mentioned the great puzzle is why were these magnificent structures and elaborate towns abandoned in favor of smaller communities after about 1450 A.D.?  Some have speculated that some catastrophe caused the people to leave. There is evidence that the area experienced significant floods between 1300 and 1450.  Those were followed by intense periods of drought.

Archeologists use multiple kinds of evidence to answer such questions, or at least shed some light on the questions posed. As a result they have been studying salt discharge on the Salt and Gila rivers, as well as the increasing soil salinity, diseases, and evidence of malnutrition. It is likely that environmental conditions changed and the Hohokam people do what all smart people do, they adapted to changed conditions. That is how people survive.

The evidence does show that the extreme flooding deepened the Gila River Channel making it more difficult for canals to carry water to fields where water levels were low. Part of the canal system was abandoned while other parts were extended miles upstream to maintain proper water flows. Around 1350 A.D., the time of the Great House, a combination of factors may have triggered a breakdown of Hohokam society and undermined their leadership.

It is probable that as a result of all of these factors, the survivors of the floods and droughts abandoned large sites like Casa Grande in favor of smaller settlements along the Gila River. Today’s O’odham people (as they are now called) believe that they are the descendants of the Hohokam people. As a result, Hohokam society never disappeared it just adapted and changed to a lifestyle that was better suited to the changed conditions. This change was likely to one more similar to their ancestors. They changed to a simpler life. Perhaps that is what we will be compelled to do.Yet as so often is the case the abandonment was likely triggered at least in part by environmental factors. Often people over do it and the land can no longer sustain the people. This has happened countless times in the Americas. To me it looks like it is happening again, but this time on a much grander scale. Large parts of the world and vast numbers of species are being degraded by human activities. This lesson seems so hard for Homo sapiens to grasp. Why is that?

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