The astronomical context of the archaeology and architecture of the Chacoan culture
Munro, Andrew M. (2011) The astronomical context of the archaeology and architecture of the Chacoan culture. PhD thesis, James Cook University.
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Abstract
Astronomical analysis of 10th to 12th century A.D. cultural evidence at Chaco Canyon New Mexico began in the 1970s. Published work includes a variety of proposals including horizon calendars, solar calendrical constructs in architecture, cardinal North-South and/or East-West (NS/EW) alignments of architecture and roads, building alignments to lunar standstills or June solstice sunrise, wall alignments to equinox sunrise or sunset, and the positioning of structures at observation points for horizon calendrical stations. Within the published archaeoastronomy work attention to Pueblo ethnography, archaeological evidence including temporal data, statistical significance, and the consideration of multiple hypotheses has varied widely. The sample of Chacoan Great Houses assessed for astronomical associations was unchanged from the mid 1990s to 2007.
There is active debate among archaeologists regarding the relative importance of political, ritual, and economic factors in the Chacoan regional system. Past archaeoastronomy work has had limited influence on such debate. Nonetheless, there is general acceptance among archaeologists of the idea that visual astronomy had a role in Chacoan culture, if for no other reason than to provide a calendrical system.
This research expands on previous samples of Chacoan Great Houses to include all those identified within "downtown Chaco," as well as a small sample of "halo" and "outlier" Great Houses. The field work, conducted under National Park Service and Bureau of Land Management permits, included compass survey, theodolite survey, and photography at a total of 28 sites. Survey results were assessed in the context of positional astronomy, Pueblo ethnography, and the archaeological record including published construction dates for the sites.
I found no convincing evidence for previously proposed architectural alignments to lunar standstills, June solstice sunrises, or equinox events. I have found that a majority of the studied Chacoan structures to conform to one or more of four architectural traditions that have astronomical associations. These include front-facing south-southeast (SSE) orientation, front facing east-southeast (ESE) orientation, alignments to the cardinal directions of North-South and/or East-West (NS/EW), and the construction of Great Houses at workable calendrical stations with horizon foresights for solstice dates. Multiple Great Houses exhibit two of these traditions in combination. A single case is identified that may incorporate three of the traditions. The "halo" Great House at Bis sa'ani includes a cardinal North-South and East-West ("NS/EW") structure, a possible SSE-facing room block, and a June solstice sunrise horizon foresight.
Building upon Hayes' and Lekson's assessments of orientations, temporal analysis of these four traditions may improve our understanding of shifting patterns of multi-cultural collaboration and dominance among ancestral Pueblo groups. A majority of the Great Houses built before A.D. 1000 are front-facing to the SSE. The SSE orientation tradition continued during the peak of Bonito Phase construction activity (A.D. 1020-1100). Most of the putative lunar standstill and June solstice sunrise alignments comprise a subset of this SSE facing group. During the same period, the first cardinal NS and EW architectural alignments were also completed. Four ESE facing Great Houses were constructed within and in proximity to Chaco between A.D. 860 and A.D. 1090. This third orientation tradition may represent some form of cultural affiliation with contemporary Rio Grande Valley people based upon comparison to previous orientation studies conducted by Lakatos, or it may perhaps represent an alternative cosmological intent.
The "new" Great Houses built during the Late Bonito phase at Chaco after A.D. 1100 are all either involved in inter-site cardinal NS alignments, or positioned at or in proximity to observing locations that can function as solstice calendrical stations. Workable solstice horizon calendars are now confirmed at Casa Chiquita, Kin Kletso, Headquarters Site A, Wijiji, Bis sa'ani, and 125 m from Roberts Small Pueblo at 29SJ 2538/2539. A potential calendrical station located in the vicinity of Peñasco Blanco's McElmo ruin is yet to be confirmed. The Late Bonito "calendrical" Great Houses may have been intended as pilgrimage destinations where people could witness a dramatic solstice sunrise or sunset. During the same time period, SSE orientation was dominant in the Totah region to the north at sites including Aztec and Chimney Rock.
The astronomical evidence presented supports the idea that people with at least three distinct cosmological intents collaborated at Chaco; it also supports Van Dyke's hypothesis that Late Bonito phase construction at Chaco represented an attempt by a weakened ritual elite to reinvigorate their legitimacy and power. The consistency of cosmological and solstitial references among Late Bonito Phase Great Houses at Chaco indicates that the Late Bonito Chacoan elite's power may have rested in part on esoteric astronomical knowledge, and an elevated cultural status for solar events.
Under the terms of a U.S. National Park Service field research permit some location-specific site data has been deliberately redacted from this document, as required by the U.S. Archaeological Resources Protection Act of 1979.
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