Culture and Ecology of Chaco Canyon and the San Juan Basin
Culture and Ecology of Chaco Canyon and the San Juan Basin
Culture and Ecology of Chaco Canyon and the San Juan Basin
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Environment <strong>and</strong> Natural Resources 57occasional crop failure from unfavorablemeteorological conditions-in particular,frost-free seasons <strong>and</strong> inadequate precipitation.At <strong>the</strong> same time, it would be easyto overemphasize <strong>the</strong> marginality <strong>of</strong> <strong>the</strong>situation. For example, by some st<strong>and</strong>ards(e.g., [E.] Adams 1979), <strong>the</strong> short, frostfreeseasons at <strong>Chaco</strong> <strong>Canyon</strong> wouldindicate "prohibitive" risks. Yet, <strong>the</strong> richarcheological record from <strong>the</strong>re suggeststhat prehistoric farming was successfulover an extended period <strong>of</strong> time. On thisbasis, it would be difficult not to consider<strong>Chaco</strong> to be closer to <strong>the</strong> optimal end <strong>of</strong> anoptimal-margin continuum or risks <strong>of</strong> yearto-yearsubsistence stress. Consideringo<strong>the</strong>r environmental variables in additionto meteorological characteristics, it seemslikely that <strong>Chaco</strong> was something <strong>of</strong> an"oasis" in <strong>the</strong> <strong>San</strong> <strong>Juan</strong> <strong>Basin</strong>, as suggestedby [Gwinn] Vivian (1970a). This in tumbrings into question <strong>the</strong> reliability <strong>of</strong>assessing marginality or suitability forfarming on <strong>the</strong> basis <strong>of</strong> modem climaticdata. In particular, <strong>the</strong> accuracy <strong>of</strong> suchwidely cited criteria as minimum growingseason requirements needs to be betterestablished before <strong>the</strong>ir implications <strong>of</strong>prehistoric adaptations can be wellunderstood. (Gillespie <strong>and</strong> Powers 1983:8)These investigators used data from <strong>the</strong> <strong>San</strong> <strong>Juan</strong><strong>Basin</strong> Regional Uranium Study (SJBRUS) database toevaluate a model that predicts use <strong>of</strong> changing relativefrequencies <strong>of</strong> sites through time, depending on <strong>the</strong>geology, elevation, <strong>and</strong> retrodicted temperature <strong>and</strong>precipitation levels. With increased summer precipitation,expansion <strong>of</strong> settlements was expected.Between A.D. 900 <strong>and</strong> 1100, for example, <strong>the</strong>re wasincreased site expansion at both high <strong>and</strong> lowelevations in <strong>the</strong> <strong>San</strong> <strong>Juan</strong> <strong>Basin</strong>, which occurs withincreased summer precipitation; during <strong>the</strong> mid A.D.IlOOs, growth halted when a 50-year period <strong>of</strong>decreased moisture impacted <strong>the</strong> <strong>San</strong> <strong>Juan</strong> <strong>Basin</strong>.Although settlements continued in limited areasaround <strong>the</strong> margins <strong>of</strong> <strong>the</strong> basin, <strong>the</strong> central areacollapsed. In <strong>the</strong> nor<strong>the</strong>rn river basins, floodwaterfarming would have been an option; in <strong>the</strong> sou<strong>the</strong>asthighl<strong>and</strong>s, dry farming would have been possible.SummaryThere is little support for major climatic changeafter <strong>the</strong> transition from <strong>the</strong> Late Pleistocene to EarlyHolocene. There were no major changes in <strong>the</strong>environment during <strong>the</strong> Holocene. However, <strong>the</strong>rehad been minor shifts in temperatures <strong>and</strong>precipitation. The change to a more arid environmentduring <strong>the</strong> Middle Holocene brought with it a changein <strong>the</strong> species <strong>of</strong> trees available; except for isolatedst<strong>and</strong>s, <strong>the</strong> ponderosa pine forest had disappeared fromChacra Mesa by 7,000 B.P. (Hall 1977). Dense pineforests were not present in <strong>the</strong> canyon, but someremnant forests did outcrop on <strong>the</strong> higher mesas, witha few trees appearing at higher elevations along <strong>the</strong>upper walls <strong>of</strong> <strong>the</strong> canyons.Pine, fir. <strong>and</strong> spruce were not abundant in <strong>the</strong>canyon for construction purposes. During <strong>the</strong> Pueblooccupation, it was unlikely that <strong>the</strong> ponderosa pinelogs used in <strong>the</strong> construction <strong>of</strong> <strong>the</strong> great house sitescould have been obtained locally; ra<strong>the</strong>r, <strong>the</strong>y wereprobably imported from some distance, where speciesgrew at high elevations; e.g., Mount Taylor, MountPowell, <strong>the</strong> Chuska Mountains, or <strong>the</strong> Cuba area (Hall1975:57, 1977). The studies <strong>of</strong> Betancourt <strong>and</strong> VanDevender (1980) <strong>and</strong> Samuels <strong>and</strong> Betancourt (1982)indicate that fir <strong>and</strong> spruce would have been importedfrom long distances, but that ponderosa pine wouldhave been available in scattered st<strong>and</strong>s in favorablehabitats. Dense ponderosa st<strong>and</strong>s were more distant,probably 40 km from <strong>Chaco</strong> <strong>Canyon</strong>. Because mostconstruction beams attributable to this species are 35em-plUS in diameter, it is unlikely that tree harvestingwould have destroyed <strong>the</strong>se st<strong>and</strong>s. The removal <strong>of</strong><strong>the</strong> larger-sized, slow-growing specimens, however,would have forced <strong>the</strong> Pueblo people to travel far<strong>the</strong>rto obtain logs <strong>of</strong> appropriate size for construction(Betancourt et al. 1986:373). Samuels <strong>and</strong> Betancourt(1982) modeled <strong>the</strong> effects <strong>of</strong> timber-cutting, whichwould have deforested <strong>the</strong> area by A.D. 900.Harvesting <strong>of</strong> pinon <strong>and</strong> juniper in <strong>the</strong> canyon,however, probably caused <strong>the</strong>ir disappearance by thatdate.Ra<strong>the</strong>r than simple lists <strong>of</strong> plant <strong>and</strong> animalspecies, we now have a record <strong>of</strong> which ones occur inspecific zones. We know something about <strong>the</strong>densities <strong>of</strong> some species <strong>and</strong> how <strong>the</strong>y respond toeven small fluctuations in rainfall by season or