About Those Chaco Burials

Old Bonito from Above

In discussing a recent paper using stable-isotope techniques to evaluate subsistence in the Southwest during the Basketmaker period, I mentioned that one of the control samples used for contextual comparisons of the Basketmaker results came from Chaco Canyon great house burials.  I don’t know how on earth the Utah-based researchers managed to get permission to test these burials, as this is a highly sensitive political issue in Southwestern archaeology in general, but somehow it seems they did, and the information they got is enormously useful in understanding some aspects of the Chaco system.  It appears to only be reported in this Basketmaker paper so far, and only as comparative data, although there is a reference to a manuscript in preparation by the same authors focused on the Chaco data specifically.  This doesn’t appear to have been published anywhere in the three years since the Basketmaker paper was published, as far as I can tell.

This type of analysis of Chaco burials is remarkable enough, but even more remarkable is that these aren’t just any Chaco burials.  Two of them are the two most remarkable burials found anywhere at Chaco and arguably in the whole Southwest: Skeletons 13 and 14 from Room 33, which had the largest and most elaborate grave assemblages known in the region.  Also included were two burials from the adjacent Room 56 and one from Kin Bineola, a nearby outlying great house which is generally described as “unexcavated” but which did see some largely undocumented digging by the Hyde Expedition in the 1890s resulting in a few specimens now in the collections of the American Museum of Natural History.

Kin Bineola from Plaza

These remains were all tested for carbon and nitrogen isotope ratios, like the Basketmaker specimens and some other comparative samples from Pueblo period sites in the Kayenta area and Canyon de Chelly.  All the samples showed carbon isotope ratios in the same general range, indicating a heavily maize-based diet.  The nitrogen ratios, however, which are used to determine the amount of meat in the diet, varied considerably, with the non-Chacoan Pueblo remains patterning with the Basketmaker examples in showing a diet with little meat but the Chacoan ones showing evidence of much more consumption of meat.  This supports what had already been suspected based on the generally healthier appearance of great house burials compared to those found in other Pueblo sites, even small-houses within Chaco Canyon, namely that the people, whoever they were, who were being buried in the great houses were not only given much more elaborate and numerous grave goods in death but were also considerably healthier in life.  This in turn provides strong support for interpretations of Chacoan society that see it as having had a strong hierarchical component, with the great house burials coming from the higher ranks of society.

That’s all well and good, and it provides important information bearing on some major questions in Chacoan archaeology, but what I find more impressive about this data is that most of the Chacoan burials (all except one of the two from Room 56) were also radiocarbon dated.  The advent of the Accelerator Mass Spectrometry (AMS) technique, which requires much smaller amounts of organic material than traditional radiocarbon dating, has made it feasible to do direct dating both on small amounts of material (e.g., pollen) and on important specimens like human remains that are too valuable both politically and scientifically to sacrifice large quantities of bone for dating.  Like similar dates that have been taken on corn cobs, these direct dates provide important chronological anchors in understanding the development of Chaco and its system.

Wall Niche, Pueblo Bonito

Unfortunately, while the paper does report calibrated 95% date ranges in addition to raw dates, it reports midpoints of those ranges (which are not very meaningful) rather than intercepts, so it isn’t really possible to get a sense of probable dates more precise than the 95% ranges.  (Also, the reported midpoints don’t appear to actually be the midpoints of the reported 2σ ranges; maybe they’re from the unreported 1σ ranges?)  Still, that’s something, and there are some interesting implications.

The one specimen from Room 56 that was dated had a range of AD 1023 to 1208, which probably puts it sometime during the height of the Chacoan era (AD 1030 to 1130) or perhaps a little later.  This is significantly later than the initial construction of this room, which took place during the earliest period of construction in the ninth and early tenth centuries, but from the ceramic types associated with the burials in this cluster of rooms it seems it was used for burials throughout the period of major occupation, so this is a very plausible date.  These bones apparently came from Room 56, and are listed in a specimen list as coming from the debris in that room, but the description of them in that list reads “Human Bones with #53 the dark ones,” and the undated specimen from the same room on that list has a note reading “Some were found in R. 53, thrown from R. 56.”  The first description is cryptic and I can’t make any sense of it, but the second seems to imply that these bones all originally came from Room 56 but some were thrown into Room 53, probably by Warren K. Moorehead during his rather crude excavations in this part of the site.  Regardless of the specifics, it seems there is little contextual information for these remains, so not much more can be said about them.

Lintels Sampled for Tree-Ring Dating, Kin Bineola

The Kin Bineola specimen has a date range that overlaps considerably with the Room 56 one but has a generally earlier range: AD 891 to 1147.  Much of the construction of Kin Bineola apparently dates to the tenth century, judging from both masonry style and the few tree-ring samples, and some seems to date to the early twelfth century, so either end of this range is quite plausible, although the bulk of evidence suggesting the importance of this site in the tenth century, a period of relative quiet for construction at Chaco itself, makes me inclined to think an earlier date is more likely.

The most interesting dates are from the Room 33 specimens.  Since these are such important burials for understanding Chaco, knowing when they were interred is very desirable.  They were the two lowest burials in the rooms and the only ones that were completely intact when excavated; the twelve burials above them were substantially jumbled, although they still had plenty of grave goods associated with them.  This implies that they were the earliest people to be buried in the room, and the pottery associated with them was relatively early but can’t be dated very precisely beyond that.  It is not clear from any of this how early they were buried, expecially whether it was before or after the major expansion of Pueblo Bonito beginning in the 1040s that may have involved substantial changes in the function of the building, perhaps including a change in the function of some rooms in the older part of the building into burial chambers.

Northwest Part of Pueblo Bonito Showing Expansion of Outer Wall

The date ranges reported here are AD 690 to 944 for Burial 13 and AD 690 to 940 for Burial 14.  Statistically these are virtually identical, and they strongly imply that the two were buried at the same time, which makes sense given their relative position and similar grave assemblages.  This is also really early, with the early part of the range extending long before the earliest known construction dates for Pueblo Bonito.  Since these clearly seem to be primary rather than secondary burials, this probably just means that the true age doesn’t lie at the early end of the 95% range.  That puts the most likely time of burial at between AD 850 and 940 or so, or between the earliest construction dates and the end of the date range.  This is still well before the expansion of the building, and it doesn’t extend much after the latest dates for the initial construction stage.

The upshot of all this is that these two burials appear to be significantly earlier than has generally been assumed.  They seem to date to a very early period in the history of Pueblo Bonito, and it’s even possible that Room 33 was initially constructed as a burial chamber for them.  George Pepper, who excavated it, thought the room had not originally been intended as a burial chamber, but he didn’t explain what led him to that conclusion.  Whatever the original function of Room 33, it seems clear from this evidence that it became a burial room very early on, and that these two enormously elaborate burials were part of Pueblo Bonito for at least the vast majority of its period of occupation.  I think this may have some important implications for understanding the construction sequence of the building and possible changes in its use over time, and perhaps even in understanding the rise and nature of the Chaco system as a whole.  Piecing together what exactly those implications are, however, will require considerably more thought and study.

Coltrain, J., Janetski, J., & Carlyle, S. (2007). The Stable- and Radio-Isotope Chemistry of Western Basketmaker Burials: Implications for Early Puebloan Diets and Origins American Antiquity, 72 (2) DOI: 10.2307/40035815