Catastrophe or something more complicated
Was it a Catastrophe…
Archaeologists used to believe that Hohokam population decline happened quickly and was caused by some type of catastrophe, such as flooding, disease, or warfare.
…or was it Coalescence?
If population decline did not result from a single catastrophe, understanding why it happened is more complicated. Archaeologists now believe the region experienced a gradual, centuries-long process of population decline. Archaeology Southwest researchers explain this region-wide decline through the Coalescent Communities model.
Gradual Population Decline: The Coalescent Communities Model
As immigrants arrived on the edges of the Hohokam region, local groups began coming together (coalescing) into fewer, larger communities, which caused economic, ecological, and social changes. One result of immigration was increasing social tension. More defensive site locations were chosen and use of small, scattered farm sites was discontinued. People increasingly focused on cultivation of a few crops in irrigated fields, and discontinued more dispersed forms of agriculture and the use of wild foods.
Dependence on irrigated crops diminished diet and health. As people grew a smaller range of foods, they were more vulnerable to environmental degradation and flooding, making farming increasingly difficult and risky. At the same time, as they began to live in more concentrated settlements around irrigation canals, increased contact among people in crowded settings, the challenges of waste disposal, and standing water increased the risks of disease.
These factors led to a slight change in the ratio of births and deaths. Based on improved techniques for dating sites and estimating population (Remember Puzzle Piece 2 and Puzzle Piece 4?), archaeologists conclude that these changes only resulted in a rate of population decline between 1% and 2% per year. Such a decline may have been barely noticeable to most people in their daily lives. An important lesson from archaeology, however, is that small changes can lead to large effects over many generations. For the Hohokam, gradual decline resulted in the loss of more than 75% of the population from the early 1300s to the mid 1400s.
The Lower San Pedro Valley
Coalescence is clearly visible in the lower San Pedro River valley, 120 miles (193 kilometers) to the southeast of Phoenix, where Archaeology Southwest conducted research at 29 sites. A small number of immigrants from the Kayenta region arrived in the late 1200s (Puzzle Piece 3). Immediately following their arrival, local communities contracted in number and grew in size, becoming concentrated near the river. At the same time, the use of small upland sites and agricultural fields was discontinued. Through the following century, population gradually declined and people discontinued use of sites in the southern part of the valley. People gradually moved to join their neighbors in villages to the north, in an effort to maintain viable communities, eventually disappearing from the archaeological record by the early 1400s.
Core Decay in the Phoenix Basin
The Phoenix Basin was the heart of the Hohokam region, and it experienced a different pattern of decline. Many of the same processes of coalescence occurred here, but early population decline appears to have been offset by the arrival of people from elsewhere in the Hohokam region, as well as immigrants from neighboring regions. As regional population began to decline, the populations of large, central sites like Pueblo Grande grew and put added pressure on local agricultural fields.
Areas near canal intakes had advantages that made them popular settlement locations through time, including first access to irrigation water and control over how it was distributed downstream. These qualities made Pueblo Grande one of the largest and most powerful communities in the valley. Archaeologists have documented signs of trouble, however: a decrease in the size and availability of wild food resources and an increase in deposits of silt and clay in irrigated fields that would have made farming difficult. Furthermore, unusually large floods along the Salt River became increasingly frequent during the mid-1300s. These would have damaged communities and fields near the river, as well as canal structures and intake locations.
By the late 1300s, sites such as Pueblo Grande were greatly diminished and their populations suffering. Unfortunately, Pueblo Grande and other large sites like it were at the core of the irrigation system where critical irrigation features such as intakes, headgates, and trunk canals were located. Other communities down-canal were inhabited by more recently arrived populations including immigrants from other regions. Even though these outlying communities continued to be viable, they depended on the maintenance of irrigation systems originating at the core sites like Pueblo Grande. As core areas fell into decay, their populations suffered the consequences of coalescence and conflict.
Conclusion for the Hohokam but not the Huhugam
Hohokam population declined due to small changes in birth or death rates over a long period of time. Diminished quality and diversity of diet led to poor health. Population concentration along irrigation canals also created a more favorable environment for the spread of disease.
Some population decline is attributable to movement of people out of the region as conditions deteriorated. Archaeological evidence—including the distributions of Roosevelt Red Ware, obsidian used for stone tools, and objects used in late Hohokam rituals—indicates that groups in the Hohokam region maintained connections with people in other areas.
As the populations of the Hohokam region continued to decline and communities became more variable in their cultural makeup (as the descendants of both locals and immigrants), it became difficult to maintain cultural traditions. There were fewer people in more dispersed communities with the knowledge required to pass customs on to younger generations. Eventually, artifacts and architecture archaeologists define as “Hohokam” disappeared—or, rather, changed and became unrecognizable. Small remnant groups no longer practiced the behaviors associated with the Hohokam archaeological culture. They were not Hohokam. Nonetheless, from a modern American Indian perspective, they were Huhugam (Puzzle Piece 1). This brings us full-circle, to an understanding of how people who were at one time both Huhugam and Hohokam ceased to be Hohokam while remaining the ancestors of today’s native people.