Culture and Ecology of Chaco Canyon and the San Juan Basin

56 Chaco Project Synthesisamined the dendroclimatological data for variables thatcould be compared to those derived frompalynological and alluvial data to determine whetherthe proposed alluviation correlated with arid periods(Bryan 1954; Karlstrom 1983) or wet periods (Love1980; and Hall 1977). He had more success with theformer. but noted that much more research is neededbefore this problem can be solved.Depending on the period under consideration.inhabitants of the Chaco area would have relied ondifferent resources that would affect their subsistencestrategies and social organization (Gillespie 1985). Ifthe mixed conifer woodland and open steppe habitatdominated by sagebrush in the Chaco area wasprobably relatively unproductive during thePaleoindian period. it is expected that the earliestpeople would have used areas farther south and eastwhere there was greater precipitation and mildertemperatures that would favor more biodiversity thanthe San Juan Basin. The Four Comers area of theSouthwest would have a smaller and more variablepopulation of large game animals and a paucity ofusable floral resources (Gillespie 1985:26). Gillespiethought that the archaeological evidence agreed wellwith this.The Middle Holocene. with its initial moistsummer conditions, was probably favorable forhunters and gatherers of the Early Archaic (Jay-Bajadaperiods). Plant and animal resources would haveincreased with enhanced summer rainfall, and pinonnuts would have been abundant for the first time.Bison may have peaked. Yet the more favorable areasto the southeast, where greater numbers of sites havebeen found, would have been preferred to the San JuanBasin. During the Late Archaic (San Jose and Armjioperiods), cooler and less mesic conditions probably ledto decreased resource availability. Because Archaicevidence from the Chaco area peaked around 3,000B.P. and cultivars are present in the sites, Gillespie(1985:32) suggested that populations responded moreto social, demographic, or other non-environmentalconditions.During the past 2,000 years, Gillespie (1985:35)suggested that the relatively warm temperatures andhigh summer precipitation from about A.D. 950 to themid-l100s would have allowed cultural developmentin Chaco Canyon to flourish. The agriculturalconditions would have been favorable. The onset ofa period of low summer rainfall in the mid-twelfthcentury may have destabilized the economic system.Gillespie and Powers (1983) examined settlementpatterns throughout the entire San Juan Basin todetermine whether changes were related to limitationsimposed by climatic parameters; e.g., elevation range,temperature, precipitation, and length of frost-freeseason. For example, the high, cool-season precipitationin the north is more evenly distributedthroughout the year. In the south, the summer peak ismore evident, with an average of 35 percent fallingbetween July and August in the Red Mesa Valley andZuni. This is 10 percent more than that recorded forthe northern San Juan Basin during this period. Ingeneral, precipitation correlates with elevation, asdoes the frost-free season.Based on their knowledge about the arid SanJuan Basin and its topography and variable rainfallpatterns, and knowing that going in almost anydirection from Chaco would improve conditions foragriculture, Gillespie and Powers made the followingpredictions:It is suggested that the relative aridity ofthe basin greatly restricts the potential fordry farming. Instead, the mid-summermoisture peak and overall aridity suggestmore reliance on cultivation in sedimentswatered by summer runoff. Anasazi farmingtechniques and field locations wereundoubtedly highly varied, but givenpresent hydrologic and geomorphologicconditions, it is believed the overallagricultural potential of the basin isdirectly related to summer rainfall. Extendedperiods of high summer precipitationin prehistoric times should correspondto use of a greater variety ofagricultural techniques in a variety oftopographic situations.In reviewing modem temperature andprecipitation parameters and their relationto accepted criteria for optimal farming,several inferences can be made. First, it isprobable that in many areas of the San JuanBasin, there exists a potential risk of