The paper by Glenn Davis Stone and Christian Downum that I mentioned in the last post, which evaluated the archaeological record of the Wupatki area of northern Arizona in the light of Ester Boserup‘s theory of agricultural intensification, was based largely on the data from an extensive archaeological survey of Wupatki National Monument done by the National Park Service in the 1980s. This data is presented in a more complete form in an earlier paper that Downum cowrote with Alan Sullivan. This paper looks at the previous models proposed for the settlement and abandonment of Wupatki in the context of the new data from the survey.
The most influential model for the prehistory of Wupatki has been that presented by Harold Colton of the Museum of Northern Arizona based on work done in the 1930s and 1940s. Colton saw the extreme aridity of Wupatki as having discouraged settlement there until the eruption of Sunset Crater Volcano in AD 1064 spread a layer of volcanic ash over the area. This ash acted as a natural mulch to retain water from the infrequent rains which would otherwise evaporate from the thin soil. Colton looked at the large number of sites that seemed to have been built in the aftermath of the eruption and saw a “land rush” in which people from all over the local area come to Wupatki to take advantage of the improved conditions for farming from the ash fall. Over time, however, the ash cinders began to blow away in the strong winds and the productivity of the land declined, so the people began to aggregate into the large pueblos for which the Wupatki area is best known. Once in these aggregated villages, the poor sanitary conditions of living in such close quarters, combined with the continuing decline of agricultural conditions, forced the abandonment of the whole area some time in the thirteenth century.
This is a plausible story on the face of it, but Colton’s account has been challenged more recently by other archaeologists who point out that a great many of the structures built soon after the ash fall that Colton included in calculating the population increase were small, ephemeral structures that probably served as field houses or other special-use locations rather than year-round dwellings. This implies that Colton was double-counting both these impermanent structures and the actual permanent houses of the people who used them, thus coming up with inflated population figures on which he based his “land rush.” The systematic nature of the survey in the 1980s provided the opportunity to determine just how many sites there really were and how many actually served as permanent dwellings.
As Downum and Sullivan tell it, the results basically vindicate Colton’s critics. The vast majority of the structures found were small and relatively impermanent, with few artifacts. In addition, a careful tabulation of sherd types at most of the sites showed that the immediate post-eruption period, far from being the land rush of Colton’s theory, was actually a time of relatively limited occupation. There were more sites from this period than from the pre-eruption period, when the area was nearly uninhabited, but still not very many. It was not until a few decades later, starting around AD 1130, that building began to really pick up, as indicated by both sherd types and tree-ring dates. The high point of construction didn’t come until the 1160s, a century after the initial eruption. (It is actually not clear how long the eruptions continued after the beginning around 1064, and there may well still have been occasional activity by the volcano this late or even later.) Construction seems to have effectively ceased by 1220, and the area was probably abandoned not long after that.
The upshot of all this for Colton’s theory is that, while it does seem to be true that the ash improved the suitability of Wupatki for agriculture, people didn’t immediate act to take advantage of this. Downum and Sullivan propose that this may have been because it took some time for the effects of the ash fall on the soil to manifest, but I think a more plausible explanation for this can be found by looking outside the immediate area to the larger region. The decades after 1130 were a time of extensive drought throughout the northern Southwest. This is when Chaco collapsed (or at least declined), and there were likely extensive migrations all around the region. In this context, people may have come to Wupatki less from the “pull” factor of the beneficial effects of the volcanic ash and more from the “push” factors of drought and/or political instability elsewhere. Of course, there were at least some people farming at Wupatki before this, so the fertility of the area may have become well known at the same time as things were deteriorating elsewhere, making both push and pull factors part of the regional dynamics.
In line with the arguments in the later paper by Downum and Stone, Downum and Sullivan here argue that agriculture for most of the period of occupation of Wupatki was extensive rather than intensive. They do claim, however, that intensification came right at the end of the occupation period, after 1220, on the basis of more intensive usage of the sites from that period based on sherd counts. This is kind of dubious, and it appears that Downum changed his mind about it in the eight years between this paper and the later one. Intensification at this can, however, be incorporated into the argument made in the later paper that intensification was impossible in this area due to ecological conditions. Once people began to leave the area, perhaps spurred by increased warfare and/or continuing climatic instability, those who remained would not necessarily have been able to secure access to the large amounts of land they had had claimed earlier as part of the consolidated political groups associated with the large pueblos in the Stone and Downum model. These few remaining farmers may then have attempted to intensify production on the smaller amounts of land available to them. Given the aridity of the area, however, this would not have worked reliably enough to allow them to stay, so within a few decades or less they would leave as well, leaving the entire Wupatki area abandoned by 1275. Note that this is when the famous “Great Drought” associated with the abandonment of Mesa Verde and other areas began, so the aggregation and abandonment processes associated with Wupatki may well have been different from the similar processes elsewhere in the Southwest.
Since I’ve been taking note of the scholarly context of the papers I’ve been discussing lately, I should point out that this one is very much an archaeology paper, and a classic processual one at that, with lots of statistics and an explicit model of interactions between people and the environment. This certainly makes it more “scientific” than, say, the later paper by Downum and Stone, which is more anthropological and not very scientific at all, but as with many such archaeological papers the scientific trappings are somewhat superficial. This is definitely not as rigorous an attempt at quantitative social science as the economics paper on plowing and gender roles I discussed a little while ago, for instance. I would therefore argue that this is only science in a somewhat questionable expansive sense, and not necessarily anthropology at all, despite the frequent claims of processualists to be doing “archaeology as anthropology.” Again, however, that doesn’t mean it’s not worthwhile scholarship. Regardless of how it’s classified, this is interesting research that can serve as a useful source of data for a variety of other studies such as the one Downum later did with Stone.
Sullivan, A., & Downum, C. (1991). Aridity, activity, and volcanic ash agriculture: A study of short-term prehistoric cultural-ecological dynamics World Archaeology, 22 (3), 271-287 DOI: 10.1080/00438243.1991.9980146