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The signs of human impact in the Sonoran Desert are all around us. Many of these impacts are the topic of other papers in this symposium. But people have been in this desert for 10,000 years. Paleoindian hunters, Archaic hunter-gathers, Hohokam farmers, Native Americans of the historic and modern periods, Spanish explorers and American pioneers all have left their mark. A review of archeological evidence of human occupation in the Sonoran Desert may highlight the impact people have had on this fragile environment and may put some of our current concerns in perspective.
Paleoindian Period (c. 9000 B.C. to 5500 B.C.) top
Our knowledge of the Paleoindian period begins with evidence of Clovis mammoth hunters at the end of the Pleistocene. These people are believed to be of Asian origin having come to North America across the Bering Straight land bridge. The hunting of large game during a period of great environmental change is documented at kill sites where distinctive fluted points sometimes are found imbedded in the bones of now-extinct mammals. Species of animal bones found at Paleoindian sites include now-extinct animals such as mammoth, large bison, horse, tapir and camel as well as present-day species such as rabbit, muskrat and bear. Some researchers hypothesize that the hunting of wooly mammoth by Paleoindians was one of the factors that hastened their eventual, albeit unavoidable, extinction.
Paleoindian sites are found in caves or eroding from the banks of arroyos. Documented sites are few in number but their distribution throughout the southwest is fairly broad. Because the sites often are buried quite deeply their visible impact on the desert is low.
Archaic Period (c. 5500 B.C. to A.D. 100) top
The hunter-gatherers of the Archaic period left a more distinctive mark on the landscape. They subsisted on hunting small game and gathering a variety of plants. By the end of the Archaic period a number of cultigens, most notably corn, had been adopted from Mesoamerica. Their artifacts include dart points, chipped-stone tools for cutting and scraping and ground-stone tools for processing plant foods.
Features of the Archaic period still visible in the desert include trails, sleeping circles, and artifact scatters. The scatters may represent quarries, tool manufacturing sites, hunting stations, or may be surface indicators of buried camp sites. Archeological excavation of sites from the Late Archaic period reveals house pits, hearths and storage pits. Some of the earliest rock art in the southwest may be from the Archaic period. Known Archaic sites are more numerous than sites from the Paleoindian period and have wide distribution in a variety of environmental zones.
The Hohokam Period (c. A.D. 100 to A.D. 1450) top
By A.D. 400 the Hohokam period is well underway. These desert farmers established sedentary villages in areas where dry farming and canal irrigation would be productive. However, they never abandoned hunting or the use of wild plants for food. Smaller, special-use sites are found in a wide range of desert environmental zones. However, it is interesting that there is little evidence of Hohokam occupation or use of high mountain zones.
What do we see when we look for the footprint of the Hohokam on the Sonoran Desert? We are looking for signs that are 500 to 1500 years old. Casa Grande and Pueblo Grande are two of the best known examples of Hohokam architecture. Platform mounds, compounds, ball courts, reservoirs, wells, canals, dry-farming features and trash mounds also are highly visible Hohokam features. Rock art is one of the most visible and dramatic manifestations of Hohokam culture.
But there are other signs that are more subtle. When I visit a prehistoric artifact scatter site that has no visible surface features I see broken pottery and stone artifacts that might tell me when a site was occupied and the range of activities that may have occurred there. When I visit the same site with a plant ecologist, a new world unfolds. The plant ecologist sees subtle changes in the vegetation that may be due to compacted soils or increased nutrients. I have been shown examples of both. top
The extensive canal systems developed by the Hohokam along the Salt and Gila rivers provided water for irrigation. Maps of the canals by Turney, Midvale and others were made before modern development and agriculture destroyed the evidence of these complex prehistoric systems. We have a picture of extensive and intensive land use one might not usually attribute to prehistoric peoples. There is evidence that some canal systems may have defined the interaction sphere of a community. In other words, there is evidence that people traded and interacted with the people upstream on a canal system that might be ten miles or more in length. The canal system that brought water to Casa Grande was taken off the river almost eleven miles upstream from Casa Grande.
Why does a canal system grow? It appears that the Hohokam knew to drain their fields to prevent salinization. Does it grow to keep up with expanding population? Does it move down the line as resources such as fuelwood are depleted? It would seem that an abundance of trash mounds and abandoned structures can make it time to abandon a site for a while. Houses can be remodeled and reused after a period of time elapses. top
Extensive dry farming systems of the Hohokam are still visible today. Stone terraces, check dams, rock piles, and other types of water control features were used to grow domestic and specialized crops such as agave. An example of this is the agave fields near the Marana Platform Mound which cover an area of five miles by one mile with more than 45,000 rock piles and two dozen roasting pits. Agave was processed for both food and fiber. Settlements in and near good agricultural lands are easy to understand but how and why did the Hohokam decide to plant and process agave in an area previously unoccupied because it was not agriculturally productive for corn and other domestics? It appears that the Marana Community was occupied for only 15 or 20 years. Perhaps there were a number of environmental constraints for such a large enterprise such as the depletion of fuelwood necessary for the roasting pits used to process the agave.
The extent of the Hohokam was quite broad coincident for the most part with the extent of the Sonoran Desert. These people were the shell traders of the southwest. Trade routes to the Gulf of California have been documented. The shell brought to the area from the gulf was transformed from raw shell to beautiful jewelry and decorative items traded as far away as Utah and Colorado. Trade implies exchange of ideas and information with trade partners. The desert dwellers knew of oceans and mountains but continued to live in this harsh but beautiful place.
Historic Period top
The Spanish explorers brought a variety of plants and animals to the Sonoran Desert. They brought horses, cattle, fruit trees and domestic crops that are still with us. They brought diseases that killed native peoples. They also brought religion that changed the ideology of many of the native inhabitants and left us with beautiful missions.
Spanish observations on the lifeways of the Native Americans they encountered have served as the first written history of these people, even if its accuracy is questionable. Their perceptions were colored by their own culture expectations. Remember also that they were the first people in North America applying for government funding and so may have exaggerated their descriptions for effect.
The Pima and Tohono O'Odham observed by the Spanish were living in small groups and traveling in seasonal rounds to different parts of the desert, following water, game and wild plants. During Kino's explorations of 1697 near Casa Grande, Manje noted salted fields with no grazing for his horses and a village that had "a high pile of wild sheep horns which looked like a hill". Is this unwise consumption of a game species or Spanish hyperbole? Probably a little of both.
Mining has caused great changes in parts of the Sonoran Desert. The early small-scale mines may not have produced much in the way of valuable minerals but they left scars and trash dumps still visible today. Cattle ranching has caused changes in plant communities. Mining and ranching are responsible for causing communities to grow up around them to provide food and other supplies. Agriculture has led to the clearing of miles and miles of natural vegetation and the use of enormous amounts of water. Interestingly, many of the historic and modern canals along the Salt and Gila rivers follow the traces of the prehistoric Hohokam canals.
The extent of modern development in the Sonoran Desert is due to these industries as well as to the energy crisis of the 1970's that sent people to warmer climates and the booming business of retirement. We have been occupying the Sonoran Desert since Paleoindian times. By Hohokam times it is clear that we have begun to use things up. What is unclear is whether or not the desert would have been able to sustain the lifeway of the Hohokam. We can still see the marks on the landscape and changes in vegetation communities that are hundreds of years old. The features and customs of the historic period are still visible and many are still in use today. But we modern desert dwellers need to accept our responsibility to educate our children, neighbors, and our clients about the impact people have had on this desert and what our best guess is about the extent of impact the desert can sustain before we all have to move on. top