Culture and Ecology of Chaco Canyon and the San Juan Basin

Environment and Natural Resources 45rainfall that affected the vegetative production alsoaffected the location and abundance of speciesavailable to hunters. Studies of the deer mouse (Peromyscusmaniculatus), a generalist forager, provideddata to examine the vegetative diversity model (thathunters and gatherers would utilize habitats whereecological diversity is greatest). J. Cully (1984b)reported that deer mice respond to between-habitatdiversity and young disperse into a variety of habitats.Deer mice populations are least stable in habitats withhigh plant diversity and most stable where diversity islow but cover type is high. Although these correlationswere not considered significant (J. Cully1984b:216), Cully suggested that the deer mice betterfit the strategy of living in an area that was near to agreat variety of resources that would be available atdifferent times (J. Cully 1984:221). This concept underliesthe mini-max theory, but without the assumptionsof the vegetative diversity model (used whereecological diversity is greatest). Based on this work,he predicted that in Chaco Canyon, Archaic huntergatherercamps would be located in the bench habitatbetween the floodplain and the shrub-grassland mesatop where a variety of resources would be availablefor harvesting during different seasons of the year.SummaryThe studies presented above indicate how climateaffects major aspects of the natural setting, yet evensmall changes in precipitation (the single largestfactor) can bring about changes in the fluvial system,as well as in the numbers and diversity of plant andanimal species. As little precipitation as 2.54 cm (1in) can bring discernible changes to the canyonlandscape. Reconstruction of past environments todetermine how much change and when would providearchaeologists with a framework within which toexamine and interpret human adaptations during thePreceramic, Pueblo, and Historic periods. Gillespie(1983, 1985) indicated the transitional positionbetween the northern and southern weather zones thataffects Chaco Canyon and the San Juan Basin. Thenext section will explore several reconstructions of thepast environment that were evaluated by Gillespie.Paleoenvironmental ReconstructionsSeveral investigators examined data from theirdisciplines to retrodict earlier conditions and suggestreasons why human adaptations changed through time.Each field of study, however, imposes certain parameterson the inferences that can be made. Geologicstudies usually discern changes in broad time scales,which can be hundreds, thousands, or millions ofyears. In contrast, dendroclimatic studies can discerndifferences in precipitation during different seasons ofa year; the resolution span for pollen data is approximately100 years. Pollen is carried in the air for longdistances or can be washed downstream for manymiles. Evidence from macrobotanical remains recoveredduring studies of pack rat middens tells usabout what was growing only in a limited area,usually one that is less than one hectare (ha) from themidden itself (Betancourt 1990:260). As a result,conclusions drawn by investigators from these fieldswill be reviewed before presenting Gillespie's (1983,1985; Gillespie and Powers 1983) climatic model,which was used by the Chaco Project to correlateenvironmental reconstruction with the early agriculturaladaptation between ca. A.D. 500 and 1300.Geomorphological ReconstructionD. Love's (1980) studies of sedimentarygeomorphology encompassed events at the largestscales discussed herein. His division of stream behaviorinto three categories, separated by thousands ofyears, indicated that only one period of fluvialgeomorphic adjustments-the intermediate-is pertinentto Archaic and Pueblo adaptations in the Chacoarea. An exact beginning date for this period was notspecified. Love (1977b:232, 1979:294, 1983b) suggested,however, that there were no major changes inthe climate or vegetation in Chaco Canyon forthousands of years. Several channels in the valleyfloor are up to 12 m deep; these formed during thelong period in which channel cutting and fillingresulted in several episodes that alternate between aflat valley floor and channel entrenchment (D. Love1979:293-296). Kirk Vincent of the USGS is currentlyrevisiting this research (Brad Shattuck, personalcommunication, 2002).D. Love (1983b:192-193) faced several problemswhen trying to determine the dates of the variouschannel cuts (Figure 2.3). He found a positive correlationbetween his data on one channel and Hall's(1975, 1977) Gallo unit (dated ca. 6,000 to 7,000B.P., see below). There was one major buried chan-