Culture and Ecology of Chaco Canyon and the San Juan Basin

------------------------------------------------------------------------------------------- --58 Chaco Project Synthesisannually. Assuming that the environment was similarover the past 2,000 years, there would have beenfluctuations in resource availability during thedifferent periods when it was either more mesic ormore xeric; and these changes would have had someeffect on human adaptations. Gillespie (1985;Gillespie and Powers 1983) has outlined what some of.these responses would have been. Jones (1972:71)and Potter (1974: 115) indicate the frailty of thevegetation in several ecological zones. Simplytrapping fauna led to disturbances in the samplingunits. Human use of the canyon would have alteredits vegetative pattern.The Chaco arroyo provided evidence of anumber of cut and fill episodes during the period ofPueblo occupation. Unfortunately, we cannot date allthe sequences. How deep the various cuts were andwhether the channel filled across the entire bottom atspecific times still need further research. If the washdegrades in sections where the angle of the fill exceedsa certain measure, then we must re-evaluate some ofthe older models for prehistoric behavior, such as thecause of abandonment of Chaco being related to slowand progressive upstream downcutting of the watersupply for both vegetation that holds down the soiland for a supply of irrigation water.DeAngelis (1972) was the first to note thelimited success of the 1930s conservation projects toretard channelization of the Chaco arroyo. The use ofdikes was more successful than some other methods.He indicated the need to better understand theinterrelationships among variables such as climate,soils, vegetation, structure and topography, drainagebasin size, stream gradient, and grazing pressure, aswell as qualitative and quantitative data, before wecould fully realize the contributions of each to theprocess. According to Hodges (1974:116-118), theconservation efforts begun in the 1930s by the SoilConservation Service were only partially successful.Planting trees in the wash and constructing dikes,checkdams, and other structures confined the water toa channel but there was further entrenching in thefloor (see Simons, Li & Associates 1982 for furtherevaluation ofthe various erosion control mechanisms).Humans would not have destroyed these forests,as Bryan (1954), Fisher (1934), Hawley (1934), Judd(1964), and others have suggested. D. Love (1979:298) also found no evidence that the inhabitants ofChaco caused arroyo formation. Although they usedsmall canals and rock quarries, possibly had smallagricultural plots on the margins of the canyon floor(Loose and Lyons 1976a), and used the arroyo as arefuse dump (Judd 1954, 1964), the data wereconsidered inadequate to demonstrate which, if any, ofthese extrinsic causes contributed to degradation of thearroyo. There was also no evidence that the downcuttingof arroyos caused the abandonment of the area.The condition of vegetation cover, although altered byhumans, affects runoff only after basic elements innature that are conductive to erosion have beenestablished. Overgrazing during the past centurywould have been a trigger for events that were aboutto occur as a function of climate (DeAngelis 1972;Hodges 1974). Deforestation and agricultural misusesof land may have been factors, but climatic factorsdetermine the amount of rainfall and its availability asrunoff.The quality of the water today is poor. Wecannot be sure what it was like in the past. Recently,park personnel have initiated a number of studies onwater quality and hydrology that may shed light onthis topic. For human consumption, the amount ofwater available in different areas of the park isunknown. Windes has initiated the placement ofseveral water gauges throughout the park; results ofhis study will provide a better understanding of thevarying amounts by season and location and the rangeof variability in the fluctuation that may have occurredover a period of years.Conflicting thoughts about the productivity ofthe soils washed in from upstream (the gray lenses)indicate a need for additional studies on com and otherplant species that were used by prehistoric farmers.Whether they were growing their own com hasrecently been questioned by Benson et al. (2003); theysuggest that much was imported from the peripheriesof the San Juan Basin.Experiments in growing com in 1977, 1978, and1979 provide some idea of what effects the variabilityin location and precipitation within Chaco Canyonmay have had. H. Tolletal. (1985:104) reported thatalthough the germination rates in all three years were