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Archive for the ‘Chaco Canyon’ Category

Black-on-white Sherd at Pueblo Alto

Black-on-white Sherd at Pueblo Alto

In keeping with what seems to be the recent pattern around here, my previous post led to some interesting discussion in the comments. Frequent commenter marcaeolog provided a link to a pdf version of Anna Shepard’s Ceramics for the Archaeologist, a classic work that challenges some of Florence Hawley’s theories that I discussed in the post. Andy Ward, who has done extensive experimental work attempting to recreate prehistoric pottery-making techniques, then chimed in with some information on his own efforts, focusing specifically on the question of what keeps carbon-based pigments from burning off during firing. Here’s part of his comment:

I have been doing research in just this area by collecting clays and firing them in open mesquite fires. While it is easier to keep carbon based paint on a pot in a reducing atmosphere this doesn’t account for polychromes. To make polychrome with a carbon based paint, like the ubiquitous Gila Polychrome, requires an oxidizing atmosphere. Certain kinds of clays have the ability to hold these carbon paints through a firing, bentonite clay in particular. Modern pueblo potters have used a slip called Cochiti slip which has these properties, ancient potters in cultures such as the Salado had access to similar slips.

As it turns out, Shepard had the same theory, based on her own experiments, which also provided solid evidence against Hawley’s theory, based on experiments with hydrofluoric acid, that it was compounds in the ash of the organic material that reacted with silica in the clay to protect the pigment from burning away. She acknowledged that this was a reasonable conclusion based on the information available to Hawley at the time, but Shepard’s own experiments comparing organic material with and without this sort of ash showed no substantial difference. Instead the biggest factor was clay type:

The most striking fact brought out by these tests is the effect of the type of clay on the permanence of the carbon. Bentonitic and other highly adsorptive clays retained a good black under firing conditions that completely oxidized the carbon on unnadsorptive, sedimentary clays. All of the clays that held the paint well required a high percentage of wafer to bring them to the plastic state and they had high shrinkage. These clays take up much more of the paint solution than the less adsorptive clays, and on drying, the clay plates are drawn tightly together, protecting the film of paint that surrounds them. The effectiveness of hydrofluoric acid in facilitating oxidation of carbon paints is explained by the fact that it attacks the clay, opening the surface and loosening the bond and thus exposing the carbon to air.

The upshot of this in cultural terms is that, contrary to what I said in an earlier post, it seems like the difference between mineral- and carbon-based black pigments is actually technological rather than cultural. Here’s Shepard again:

The relation of the type of clay to the depth of color of carbon paint from a plant extract is not a matter of merely theoretic interest to the technologist. It has a bearing on the distribution of this class of paint because it could not be produced in regions lacking adsorptive clays unless such clays could be obtained in trade. The use of plant extracts is not open to free choice or established merely by custom; it is limited by ceramic resources.

This is particularly interesting given the well-documented expansion of carbon-based pigments at the expense of mineral ones over the course of the late prehistoric period. If special clays were required to make this work, and those clays had restricted distributions, what accounts for the change? In areas that switched from mineral to carbon paint, such as Chaco, was this the result of a change in clay sources? The discovery, perhaps due to increased contact with other areas that had long used carbon, of which local clay sources worked for this? Importation of clay? Importation of finished pots? This raises a lot of questions, which to my knowledge have not received much attention in the archaeology of these areas, despite the fact that it’s now been several decades since Shepard’s research.

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Hachured Potsherds at Casamero Pueblo

Hachured Potsherds at Casamero Pueblo

When I was working at Chaco, people would ask me a lot of questions. I usually knew the answers, but when I didn’t I was quite upfront about saying so. I would often try to find out the answers to questions that had stumped me, but I didn’t always succeed, and many of those questions are the ones that I remember best, even now.

One of those questions had to do with the black-on-white pottery that is a hallmark of Chaco. A guy once asked me what they had used as a fixative to get the paint to adhere to the pottery, and I didn’t know. I didn’t really make much of an effort to find out then, as I didn’t really have any idea where to look. Recently, though, I’ve read two papers that shed interesting light on this question. Understanding them, though, requires some background on Pueblo pottery in general.

Hachured Potsherd at Pueblo Alto

Hachured Potsherd at Pueblo Alto

Basically, there are three main types of paint that were used in the prehistoric Pueblo Southwest. Two of these were in use during the period when Chaco was occupied: mineral and carbon. (The third, lead glaze, wasn’t used until later.) Both were used to produce a black color. Other colors were occasionally produced by a variety of means, but for this period black was the overwhelmingly dominant color of painted ceramics. It’s generally possible for experienced archaeologists to tell mineral and carbon paint apart by sight. Although they both tend to look black on a well-fired pot, there are various subtle differences between the two.

Carbon paint is basically just plant material, usually Rocky Mountain beeweed or tansy mustard, boiled down into an extract and applied to the pot. Mineral paint is made of ground iron-rich minerals, usually hematite, mixed with either water or an organic extract similar to those used alone as carbon paint, and sometimes with clay as well. Both types have been used both in prehistory and among the modern Pueblos. However, there were some marked patterns to usage of the different types of paint both geographically and temporally. Overall, the trend was of increasing use of carbon rather than mineral paint over time, spreading from west to east. Chaco ceramics at the height of the Chaco phenomenon in the eleventh century AD were overwhelmingly mineral-painted, while Chuska and Mesa Verde ceramics, while very similar in decoration and imported to Chaco in large numbers, were generally carbon-painted. Around AD 1100 there was a marked shift, and even Chaco pottery began to be primarily carbon-painted. By the 1200s use of mineral paint only continued in areas on the eastern and southern fringes of the Pueblo world. Distinguishing between carbon and mineral paint is thus quite useful for making inferences about culture history during this period. (In subsequent periods things became much more complicated with extensive long-distance migration and the introduction of glaze paints.)

Sherd with Checkered Pattern, Kin Klizhin

Sherd with Checkered Pattern, Kin Klizhin

Both of the papers I mentioned above are about using more formal means than visual criteria to tell mineral and carbon paint apart. One, by Joe Stewart and Karen Adams, used a scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDS) system to differentiate the two based on the amount of iron detected in the pigment. The other, by Robert Speakman and Hector Neff, used laser ablaction-inductively coupled plasma-mass spectrometry (LA-ICP-MS), a simpler and potentially less expensive method to distinguish between the two types of paint based on the concentrations of various elements. Both found that the methods they used came up with similar results to traditional visual methods, and were superior for certain sherds with unusual mixes of characteristics that made them visually ambiguous. Speakman and Neff also found a surprising amount of variety in elemental composition even within the “carbon” and “mineral” groups, suggesting that there were multiple “recipes” used to mix paint in prehistory, not just the two broad categories. This isn’t all that surprising given that this is clearly the case in modern times based on ethnographic data, but it’s still interesting.

That’s all well and good, but one thing that occurred to me in reading these papers was that it’s not at all clear why there would be multiple paint recipes, since they all ended up with pretty much the same result and some were definitely more complicated than others. This is particularly the case when considering mineral paint, since in many cases it appears that it was actually mixed with the plant concoctions that were in other places used independently as carbon paint. If boiling down beeweed produced a perfectly suitable black paint, why bother adding hematite? This might well explain why the trend over time was from mineral to carbon paint, but it’s still unclear why mineral paint originated in the first place. It does not appear to have predated carbon paint overall, at least at Chaco, where both carbon and mineral types are present as early as Basketmaker III.

Hachured Potsherds at Kin Ya'a

Hachured Potsherds at Kin Ya’a

The lack of obvious functional reasons for preferring mineral to carbon paint suggests that the choice may have been more a matter of cultural tradition, which is interesting and implies that some sort of cultural differentiation may have been present quite early in the prehistory of the northern Southwest. This isn’t really surprising, as there is plenty of other evidence for this, but teasing out the implications of all these different lines of evidence pointing to differentiation in material culture is a task that archaeologists have only recently begun to take on. It should be interesting to see what more we have to learn from these differences.
ResearchBlogging.org
Speakman, RJ, & Neff, H (2002). Evaluation of Painted Pottery from the Mesa Verde Region Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) American Antiquity, 67, 137-144 DOI: 10.2307/2694882

Stewart, JD, & Adams, KR (1999). Evaluating Visual Criteria for Identifying Carbon- and Iron-Based Pottery Paints from the Four Corners Region Using SEM-EDS American Antiquity, 64, 675-696 DOI: 10.2307/2694212

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Mt. Taylor from Chaco

As I’ve discussed before, the patterns of use and importation of chipped stone at Chaco are somewhat puzzling. Unlike many other commodities, such as wood, corn, and pottery, which were imported from specific distant locations within the Chacoan sphere of influence in astonishing quantities during the height of Chaco’s regional power, chipped stone seems to have been largely a mundane, utilitarian concern. Throughout all periods of Chaco’s occupation most chipped stone was local. At Chaco’s peak of power and influence between AD 1020 and 1130 there was a slight uptick in imports of stone, particularly a distinctive pink chert from the Narbona Pass area to the west.

As I noted in the earlier post, however, obsidian follows a different pattern from the other imported stones. It is most common not at the height of Chaco’s regional power in the eleventh century but much earlier, in the Basketmaker III period between AD 500 and 750, when it is the most common nonlocal type of chipped stone. This was a time when Chaco may have seen an earlier period of regional importance, although figuring out what was going on at this time is very difficult for several reasons. By the Pueblo I period the amount of obsidian seems to drop precipitously, and it doesn’t start to recover until the very end of Chaco’s period of Pueblo occupation after AD 1120. This pattern puts obsidian decidedly out of phase with most other material culture imports to the canyon, which tend to correlate with the well-known evidence for social complexity and monumental architecture that we associate with the Chaco Phenomenon.

A recent paper by Andrew Duff, Jeremy Moss, Tom Windes, John Kantner, and Steven Shackley tries to put the obsidian evidence on a firmer footing by using geochemical sourcing to identify the source outcrops for a broad sample of obsidian found at Chaco and at various Chacoan outlier communities in the San Juan Basin. As they note, this is the latest chapter in a complicated story. Way back in the 1980s, the Chaco Project did an extensive sourcing study of obsidian found in its excavations in the canyon using X-ray fluorescence (XRF), a non-destructive sourcing technique that was then relatively new in archaeology. Their results, reported by Cathy Cameron in a number of publications, were surprising. They seemed to show that the closest source of obsidian, Mt. Taylor, provided very little of the obsidian found at Chaco (about 4%), while a distant source, Red Hill in Catron County, New Mexico, provided a very high proportion, especially in the assemblages from earlier sites. Also well-represented was obsidian from the Jemez Mountains, the second-closest source, with the proportion of Jemez obsidian increasing over time, a common pattern in the northern Southwest.

This seemed to indicate that there were substantial early ties between Chaco and the Red Hill area, far to the south but still just barely adjacent to some known Chacoan outliers. This result was mentioned in many publications on Chaco over the years, although many people didn’t really seem to know what to think of it. However, it soon began to be questioned. After this initial sourcing study had been done, Tom Windes submitted some samples of obsidian from Pueblo Alto and the Spadefoot Toad site for obsidian hydration dating, which involved a sourcing analysis as an intermediate step in the dating process. These analyses were inconclusive when it came to dating the artifacts (not uncommon in the Southwest, where obsidian hydration has a poor record as a dating technique), but the sourcing portion suggested strongly that the samples that had previously been sourced to Red Hill instead came from Mt. Taylor. Windes mentioned this anomaly in his site reports, as did Cameron in her subsequent publications on the subject, but a full published account didn’t appear until this new study.

The new study also used XRF to do the sourcing analysis, but both analytical techniques and source characterizations have improved considerably since the 1980s, so the results were quite different from the first effort. For some reason this study was unable to do a complete reanalysis of the earlier samples (although it implies that this may be possible in the future), so there was only limited overlap and the focus was mostly on recent samples collected by Windes at Basketmaker III and Pueblo I site in and around Chaco, as well as outlier sites studied by Kantner in the Red Mesa Valley near Mt. Taylor and by Duff at the southern edge of the Colorado Plateau near Red Hill.

The results were not really surprising, in that they have been known in broad outline since Windes submitted his samples for dating and reported on the sourcing anomalies, but it’s nice to see them formalized in a peer-reviewed paper. Basically, this study found that no samples from Chaco came from Red Hill, although a few came from other sources in the same general area, and that the most common source found at Chaco was Mt. Taylor. Over time there was a trend in the Chaco data showing a shift from Mt. Taylor to Jemez sources, accompanied by the well-known trend toward less obsidian in assemblages overall. The sample from the Blue J site near Mt. Taylor, in contrast, showed high proportions of Mt. Taylor obsidian increasing over time, in marked contrast to the Chaco pattern. The southern sites showed assemblages of obsidian almost entirely composed of Red Hill and other nearby sources.

Basically, the overall pattern was a classic distance-decay distribution, where the prevalence of a given source at a given site was mostly predictable by the distance between the source and the site. This is in sharp contrast to the pattern for many other imported goods at Chaco, which are present in high quantities in the source areas and at Chaco but not in between. This suggests strongly that obsidian was not part of any general Chacoan exchange system(s) but was procured by individual communities in accordance with their own needs, mostly using the closest sources. This is in keeping with the general tendency for chipped stone to be a relatively low-priority commodity in these societies.

The paper mentions the decline in overall abundance of obsidian after the Basketmaker III period at Chaco, but doesn’t spend much time discussing it beyond saying this:

The overall decrease in obsidian use noted at Chaco sites may reflect a shift in technological focus away from hunting and a subsequent focus on grinding technology as agriculture becomes the dominant subsistence strategy.

As I’ve noted before, this is almost certainly wrong; the decrease in question occurs at the end of the Basketmaker III period, at which time there is considerable evidence that Southwestern populations were already heavily dependent on agriculture. The decrease in obsidian is still odd, though. One thought I’ve had to explain it is that maybe the obsidian from after this period isn’t actually missing at all, but is at Pueblo Bonito, which had lots of obsidian but was excavated a long time ago using techniques that aren’t really comparable to the modern techniques used by the Chaco Project and later efforts that resulted in the collections being analyzed here. I would suggest that an XRF sourcing analysis of the Bonito obsidian would be interesting. As it is, there’s a huge shift in the proportions of the different sources at Chaco between Basketmaker III and Pueblo I. The earlier samples (dominated by the huge samples from the major villages of Shabik’eschee and 29SJ423) show a predominance of Mt. Taylor obsidian, while the later ones show mostly Jemez sources. The sample size is so much smaller for the later period, however, that I’m skeptical about taking this flip at face value. Including the Bonito assemblage might help to bridge this gap, or at least explain it.

Finally, it’s again noteworthy how unimportant obsidian appears to have been to the Chaco system. Even if the Pueblo Bonito evidence ends up indicating a more important role at Chaco itself, the various outlier communities appear to have used local sources and to have followed their own priorities in acquiring this commodity rather than getting it through any Chaco-controlled or -oriented system. This is one of the ways that Chaco appears to diverge from Mesoamerican societies, despite recent evidence that it may have had more contact with them than was previously believed. Obsidian was hugely important symbolically in Mexico, and control of major sources was a major source of power and wealth for various Mesoamerican polities. In the Southwest, however, nobody seems to have cared that much about controlling major obsidian sources, and obsidian seems to have been distributed as a fairly ordinary commodity without any particular symbolic importance. I think this is one of the strongest pieces of evidence suggesting that whatever influence Mesoamerican societies may have had on Chaco was indirect and mediated by Chacoan elites rather than imposed directly from Mexico, as some have argued.

In any case, while this isn’t really the most exciting paper, it’s still an important one in straightening out a part of Chacoan archaeology that had become pretty confused. Obsidian may not have been all that important at Chaco, but it’s still worth studying in part precisely because of its mundanity.
ResearchBlogging.org
Duff, Andrew I., Moss, Jeremy M., Windes, Thomas C., Kantner, John, & Shackley, M. Steven (2012). Patterning in procurement of obsidian in Chaco Canyon and in Chaco-era communities in New Mexico as revealed by X-ray fluorescence Journal of Archaeological Science, 39 (9), 2995-3007 DOI: 10.1016/j.jas.2012.04.032

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Richard Wetherill’s Grave

Today is Wetherill Day, the anniversary of Richard Wetherill’s death in 1910, and as such I would like to continue my tradition of marking the occasion by discussing the complicated and often misunderstood legacy of Wetherill, the pioneering amateur archaeologist who excavated many sites in the Southwest, including most famously Pueblo Bonito at Chaco Canyon. I’ve talked about the general story and context in previous posts, so this time I’d like to note one specific example of how, in contrast to his popular image as a simple pot-hunter focused on collecting artifacts, Wetherill made some quite perceptive (though not necessarily correct) deductions about cultural history based on his excavations.

After his early work in the 1880s at Mesa Verde, near his family’s ranch outside the small town of Mancos, Colorado, but before his more famous work at Chaco between 1896 and 1901, Wetherill did some exploring of the cliff dwellings of the Grand Gulch area of southeastern Utah. By this point in his career Wetherill had become quite sincerely interested in archaeology not just as a source of articles to be sold but as a window into the past, and his techniques of both excavation and interpretation had improved markedly, in part due to influence by the Swedish archaeologist Gustaf Nordenskiöld, who had come to Colorado in 1891 and assisted with the Mesa Verde work.

In the winter of 1893–1894, Wetherill organized an expedition to Grand Gulch with the financial backing of the wealthy New York brothers Benjamin and Talbot Hyde. This was the first instantiation of the Hyde Exploring Expedition, which would later become the aegis for Wetherill’s work at Chaco as well. As James Snead notes in an article on the relationship between Wetherill and the Hydes:

The principal archaeological discovery of the season was of remains predating those of the “cliff dwellers,” which Talbot Hyde, exercising a prerogative of sponsorship, named the “Basket Makers.”

And Basketmakers they remain; the term is still in use to designate this culture, which did indeed predate the later groups of “cliff dwellers” who built stone houses and are therefore known as “Pueblos.”

But how did Wetherill and the Hydes know that the Basketmaker remains they found at Grand Gulch predated the cliff dwellers? Through the use of stratigraphy, which is based on the assumption that in undisturbed deposits lower layers are older than higher ones. The Basketmaker deposits were below the cliff dweller ones, therefore they were older. There have been suggestions that Wetherill actually used stratigraphic excavation at this time, which is to say that he used stratigraphic levels as the organizing principle for the excavation itself, but David Browman and Douglas Givens argue in an article on the rise of stratigraphic excavation in American archaeology that there is no evidence he actually did. Instead, he most likely excavated and only afterward looked at the strata in the exposed trenches to make his cultural determinations, a fairly common practice at the time which Browman and Givens call “post facto stratigraphic interpretation” and oppose to the truly stratigraphic excavation that arose in the 1910s.

But Wetherill didn’t just notice that the Basketmaker remains were different from and lower than the cliff dweller ones. He also came up with a tentative theory on the relationship between the two groups. Based on both artifact differences and, as Erik Reed discusses in an article on the early history of physical anthropology in the Southwest, skull shapes, Wetherill concluded that the two groups were “racially” distinct, with the implication that the one was not descended from the other. As Reed notes, this was challenged a bit by other archaeologists at the time, but later discoveries seemed to confirm it, and it became dogma in the early twentieth century until further research in the 1940s showed that the differences in skull form were actually due to artificial cranial deformation in the later skulls probably caused by the introduction of stiff cradleboards. It was further found that there were actually multiple kinds of such deformation, of possible significance in delineating different cultural groups. Reed says:

The very significant distinction between lambdoid and vertical occipital cranial deformation was brought out only in 1937, by T. D. Stewart, followed up by my 1949 paper; but was foreshadowed by Richard Wetherill who stated […] “that there is a difference in the mode of flattening the head. In the skulls of the mesa dwellers the artificial depression of the posterior part of the cranium has been applied obliquely from above, so that it principally affects the parieto-occipital region; the skulls from the cliff-dwellings have been flattened straight from behind, the occipital region being most affected.”

The distinction between the Basketmakers and cliff-dwellers on stratigraphic grounds was an important discovery, and while it was the sort of thing that many professional archaeologists would likely have noticed at the time, it’s not something a typical pot-hunter would have cared much about. Wetherill, however, not only noticed it but drew some reasonable if ultimately erroneous inferences about population history from it. He also noticed some subtle differences in skull form and attributed them to different types of cranial deformation, which was later found to be quite correct (although note that he doesn’t seem to have considered that this might have been the reason for the differences between Basketmaker and later skulls as well). Wetherill was a problematic guy in a lot of ways, as my previous posts have noted, but when it comes to archaeological methodology and inference he was definitely at the forefront of the archaeological thought of his time, if not in fact ahead of it.
ResearchBlogging.org
Browman, David L., & Givens, Douglas R. (1996). Stratigraphic Excavation: The First “New Archaeology” American Anthropologist, 98 (1), 80-95 DOI: 10.1525/aa.1996.98.1.02a00080

Reed, Erik K. (1963). The Beginnings of Physical Anthropology in the Southwest Journal of the Arizona Academy of Science, 2 (3), 130-132 DOI: 10.2307/27641802

Snead, James E. (1999). Science, Commerce, and Control: Patronage and the Development of Anthropological Archaeology in the Americas American Anthropologist, 101 (2), 256-271 DOI: 10.1525/aa.1999.101.2.256

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Chaco Wash and Escavada Wash Near Their Confluence

I’ve never read any of Jared Diamond‘s books, so I’ve been reluctant to say much about him and his ideas.  Chaco is one of his main case studies in Collapse, however, so I really should read it at some point and try to figure out what I think of it.  I’ve heard conflicting things about how accurately it presents and interprets the evidence he gathers from archaeologists.  A lot of people seem to really like it, but most archaeologists seem to hate it and think that it’s riddled with errors.  I browsed through it a little once in the Chaco bookstore (which, yes, carries it, or at least did at the time), and I didn’t see any obvious errors of fact in the parts of the Chaco chapter I looked at, but the caption for one of the pictures, an overview of the canyon as it appears now, seemed to imply that the current desolate look of the area was the result of the overexploitation of the local environment by the Chacoans, which presumably led to their collapse.  My understanding of Diamond’s message, based mainly on the subtitle of the book (“How Societies Choose to Fail or Succeed”), is that the main driver of collapse he sees is environmental degradation, and the book’s popularity in environmentalist circles certainly makes sense in this light.

In any case, I’m skeptical about the whole idea that Chaco “collapsed” in the way that Diamond seems to think.  I’ve put forth my case in detail elsewhere and won’t repeat it now, but the basic idea is that what happened at Chaco is more complicated than a simple catchword like “collapse” (however it’s defined) implies.  On the narrow point of whether whatever happened at Chaco was the result of “choices” the Chacoans made about whether to “succeed or fail,” I guess it depends on what choices you mean by that.  David Stuart argues that the rigid, hierarchical social structure that allowed Chaco to become so impressive in the first place made the system too brittle to withstand severe climatic fluctuations, with the result that it was replaced by the more egalitarian and resilient social structures of the modern Pueblos.  He sees some clear lessons for our own society from this, primarily about the problems with economic inequality (a timely topic these days).  That’s one way of looking at “collapse.”

Southeast Corner of Pueblo Bonito

I’m not sure if it’s what Diamond is talking about, though.  I’ve seen him described as an “environmentalist” in the old sense, i.e., an environmental determinist who sees major aspects of human societies as inevitable results of their environmental situations, with the twist that he obviously doesn’t have a completely deterministic view of human reactions to the environment but rather, more in line with the modern meaning of “environmentalism,” he recognizes that the interaction between humans and their environments goes both ways.  Under this view, presumably the most enlightening examples of past “collapses” to look at for insights into how we should address our own environmental problems are those where collapse was the result of ecological “overshoot,” or human use of natural resources outstripping the ability of the environment to provide them.  Joseph Tainter, who knows a lot about “collapse” from an archaeological perspective, has vigorously criticized Diamond’s (and others’) use of this approach, and I think choosing Chaco as an example of this type of collapse is particularly questionable.

It’s not that the Chacoans didn’t have major effects on their local environment.  The permanent resident population of the canyon may not have been very large, but it’s not an area that’s exactly abounding in resources, and the fact that the Chacoans imported all kinds of stuff from outside the canyon strongly implies that there wasn’t enough of all sorts of things locally to support the community.  I believe Diamond makes a big deal specifically out of the evidence for importing wood from the distant mountains, which I presume he sees as evidence that the Chacoans had deforested their local area more or less completely, with the attendant implications for overshoot and collapse.  Hence the caption on the picture I noticed when leafing through the book: the implied sequence of events is rise of Chaco leading to deforestation leading to collapse leading to a treeless desert wasteland even 1000 years later.

Intact Roof at Pueblo Bonito

But of course the evidence for importing timber from 50 miles away also implies that the Chacoans had the ability to organize some seriously impressive procurement for those resources they were lacking locally (whether because they had outstripped them or because they were never there to start with).  It’s not that they didn’t deforest their local area; they totally did, and fast!  But if that had been enough to make the system collapse, it never could have gotten going in the first place.  The abiding mystery of Chaco, after all, is not that a major center of its scale arose in the Southwest but that it arose where it did, in one of the least inviting environments in the whole region.  Somehow, the people at Chaco were able to marshal the resources of a much bigger area with many more resources, until suddenly they couldn’t.  The thing that needs to be explained by any “collapse” narrative is why that social power stopped so abruptly, which presumably also requires an answer to the question of how it developed in the first place.  We don’t know the answers to any of these questions, which is why Chaco remains such a fascinating and mysterious place even after over a century of intensive study.

“Overshoot” is not a very helpful explanation in this context.  Stripping the canyon of all its productive potential clearly didn’t lead to the collapse of Chaco, as the Chacoans were able to draw on the much greater potential of the whole region, at least for a while.  Overshoot doesn’t really explain why that control ended, either, since the overall resources of the region that the Chacoans apparently had access to were much too abundant for them to deplete.  They easily deforested the mesas above the canyon, but they never came close to deforesting the Chuskas or Mt. Taylor.  Those are big mountains, covered in trees!  And the same goes for all the other imported goods.  You could perhaps make a case for overshoot in some particular area perhaps contributing to the collapse of Chacoan power in some roundabout way, but it would definitely not be as simple as a straightforward story of overshoot leading to collapse implies.  That picture doesn’t show the enduring effects of Chacoan deforestation on the canyon; it shows what the canyon probably looked like when the Chacoans first encountered it.  Indeed, the canyon ecosystem we see today is the result of over fifty years of protection from grazing, and over a hundred years of protection from most other impacts.

Juniper Trees on the South Mesa Trail

So those are my thoughts on Diamond, and I really should read the book at some point to get a better sense of what he actually argues and whether this is a fair interpretation.  What I find interesting, though, is that noted archaeological iconoclast Steve Lekson has recently written an impassioned post in support of Diamond.  He points out that most archaeologists seem to hate Diamond’s books and spend a lot of time pointing out the flaws in them, but he argues that doing this is missing the more important point:

I’m sure there are errors – real errors.  Any work of this scope will have errors.  But much of the carping seems to concern not facts, but interpretations.  Diamond necessarily works from other archaeologists’ interpretations and I suspect the authors upon whom he relies would have something to say about all this.  The interpretations he accepts are not necessarily wrong; they are simply inconsistent with those of his critics.

I’m not saying that Diamond gets it “right.”  It’s hard to get things completely “right,” especially in science when many very reasonable hypotheses are probably wrong.  But the vehemence of academic reaction to Diamond is, I think, far disproportionate to his sins – sins of omission, commission or (worst of all) failure to cite the critic.  It is my opinion that much of the heat comes from Diamond’s success as a popular writer.  It’s not jealousy — well, maybe a little: after all, the guy won the Pulitzer with our data.  We don’t want anyone else to tell our story, even though we almost never tell it ourselves – accessibly.  And, it must be said, there is antipathy, even hostility from academics towards popular writers, even when that popular writer is an academic.     We all should re-read Article 4 of the SAA’s Principles of Archaeological Ethics, especially the bit about “Archaeologists who are unable to undertake public education and outreach directly should encourage and support the efforts of others in these activities.”

Fair enough.  I do obviously agree with the value of outreach and it’s true that Diamond has been a wildly successful popularizer of archaeology.  Lekson goes on to give a very interesting account of what he sees as the important “collapses” in Southwestern prehistory.  I note that Chaco, specifically, doesn’t appear on the list, although the depopulation of the Four Corners around AD 1300 does.  I have my doubts about that one too, but it really depends a lot on how you define “collapse.”  It’s not clear if Lekson has actually read Diamond’s book(s) (although obviously I’m hardly one to judge on that score), and he doesn’t directly address any of Diamond’s claims or interpretations about Chaco specifically, even though he is of course much more of an expert on Chaco than either Diamond or me.  Still, his general points about the reaction to Diamond are fair.  It would probably be more helpful for archaeologists who object to interpretations of their data put forth in popular accounts like Diamond’s to explain their objections in similarly popular fora, rather than just whining amongst themselves.  Diamond’s work may have a lot of problems, but at least he’s trying to draw conclusions from archaeological data and apply them to modern issues in accessible way, which is much more than you can say for most archaeologists, with a few notable exceptions like Stuart and, to a lesser extent, Lekson himself.  In any case, I think it’s clear that this conversation is really just getting started, so anyone who is really upset by the direction it’s taken so far has plenty of opportunity to jump in and contribute a different perspective.

View from Doorway at Pueblo del Arroyo

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Chaco Preservation Crew Repairing Masonry at the Fort Site

Today’s Albuquerque Journal has an article, originally published in the Gallup Independent, about the Chaco preservation crew and their work maintaining the various sites in the park.  The article focuses specifically on recent work they’ve done at Pueblo Pintado.  I don’t have a whole lot to add, but it’s an interesting account that addresses some of the complications of doing this sort of work for traditional Navajos, who have a strong taboo against even visiting Anasazi sites.  The article says that the crew deals with this in part by conducting prophylactic ceremonies before starting work on the sites, which I hadn’t known.  These ceremonies are apparently led by Harold Suina, a member of the crew who is from Cochiti Pueblo and is not Navajo (although I believe his wife is, and they live near Chaco in an area inhabited almost entirely by Navajos).  The article doesn’t say this, but I suspect that Harold’s role is particularly important since Pueblos like Cochiti have different attitudes toward the sites at Chaco than Navajos do, so he may not feel as uncomfortable dealing with them as the other members of the crew, all of whom are Navajo, do.  Not all of the Navajo members of the crew are traditional, however; some are Christian, as are many Navajos in the Chaco area, and they may not have the same qualms about their work that their more traditional colleagues have.

Anyway, it’s an interesting article, and it’s nice to see the preservation crew getting some media attention.  They do crucial work for the park, but it rarely gets noticed by either visitors or the many people who have written books and articles about Chaco over the years.  When I was doing tours I would usually do a fairly detailed description of the preservation work early on in the tour, both because people often want to know how much of what they see at the sites is reconstructed (at Chaco, very little, unlike at many other parks) and because I wanted them to appreciate how much work it is to maintain the sites and why it is therefore important for them as visitors to treat them respectfully and minimize the amount of damage they cause.  Hopefully this article will serve a similar function for a wider audience.

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"Supernova" Pictograph

Happy Fourth of July, everyone.  The Fourth is actually a pretty important date for the study of Chaco, but in a roundabout (and somewhat controversial) way.  It all has to do with a very famous pictograph panel below Peñasco Blanco at the west end of the canyon.  While the interpretation of this panel is a matter of considerable debate, one way it’s been seen is as a record of an astronomical event that is known to have occurred during the height of Chaco’s power and influence: the supernova of 1054, which formed the Crab Nebula.

We know from several Chinese reports that the “guest star” resulting from the supernova first appeared on July 4, 1054 and continued to be visible day and night for almost two years.  There are a few Japanese records of the supernova as well, along with one report from the Arab world.  No clear-cut and unambiguous accounts are known from Europe or elsewhere in the world, although a few rock art panels in the Southwest have been proposed as representing the event.  The most famous of these is the one at Chaco, which is often referred to as the “Supernova Pictograph” (even by the park itself in a sign at the site).  It consists of three symbols painted onto the rock face in red: a hand, a crescent, and a starburst-like shape.  It’s the starburst that has been interpreted as representing the supernova itself, of course, and the crescent has been seen as representing the crescent moon.  On the morning of July 5, the moon, which was a crescent at the time, would have appeared in roughly the same relationship to the supernova, as seen from the pictograph site, as the relationship between the two symbols on the panel.  Furthermore, the handprint points in the direction one would have looked to see this at at the time.  The combination of the three symbols together, plus the fact that this would have happened at a time of considerable activity in the canyon, has led some to suggest that this pictograph panel was created to commemorate this historic event.  The specific location may have been an established sun-watching position, from which the new star was seen unexpectedly and recorded.

Sign at the "Supernova Pictograph"

It all sounds fairly plausible as it goes, but there are some problems with this theory.  Probably the biggest problem is that the specific set of symbols on the panel is known from ethnographic evidence to have been used by the Zunis to mark generic sunwatching sites, with the crescent representing the moon, the starburst representing the sun, and the hand marking the location as sacred.  Now, it’s certainly possible that these symbols came to be associated with this activity as a result of the observation of the supernova at this site, but as far as I know there’s no reference to the supernova in ethnographic descriptions of astronomical observation at Zuni or any of the other modern Pueblos, so this is a pretty tenuous claim.

Furthermore, while the 1054 supernova would certainly have been noticeable at Chaco, there was an earlier supernova in 1006 (also recorded by the Chinese, and possibly by the Hohokam in southern Arizona) that was much brighter, and it’s not clear why the Chacoans wouldn’t have recorded that one too.  It took place before the Chaco system really got going on a regional scale, but there was plenty of activity in the canyon during the 900s, so people there would presumably have seen it.  It’s possible that it was recorded too, at some other site that hasn’t been found or that has disappeared in the thousand years that have elapsed since the event (note that the existing Supernova Pictograph has only survived because it was under a protective overhang), but again, there’s not any evidence for this.  The Chacoans are definitely known to have kept careful track of regular patterns in the skies, such as the solstices and the lunar standstills, so they surely would have seen unusual events such as supernovae, but it’s not clear how they would have reacted to them or how inclined they would have been to record them.

View Looking East from "Supernova Petroglyph"

So it’s not really clear how to interpret the Chaco pictograph.  I think the balance of evidence at this point leans slightly against it being a representation of the supernova, but I could be talked out of that position if some additional evidence for the supernova theory can be found.

Others, however, have proposed even more extreme theories based on the 1054 supernova.  Among the more noteworthy of these is a proposal by Timothy Pauketat and Thomas Emerson, in a 2008 article in the Cambridge Archaeological Journal, that the rather sudden florescence of the Cahokia site in Illinois around AD 1050 may have had something to do with the supernova.  The theory they present is interesting, but hard to effectively support.  For one thing, dating methods in the Midwest are much less precise than in the Southwest, so pinning down any event to the year is usually not possible.  There is certainly a suggestive correspondence between the sudden rise of Cahokia and the supernova, however, and this is supported by the apparent use of stellar imagery and symbolism at Cahokia and the importance of the stars to later cultures in the area, so there may well be something to this.

Opening at Casa Rinconada That Channels Sunbeam at Sunrise on Summer Solstice

I’m a bit troubled, however, by the reliance of Pauketat and Emerson on evidence from Chaco and the way they interpret it.  For one thing, they say that the Supernova Pictograph is “above” Peñasco Blanco, when it’s actually below it, and not visible from the great house itself.  More importantly, they say of the effect of the supernova:

Some believe that this particular cosmic event, which left behind the Crab Nebula, was commemorated in architecture and iconography at the time or in subsequent years. The most compelling evidence for this comes not from the Cahokia region but from the American Southwest, where a tree-cutting date places the construction of the largest and most isolated ceremonial building in Chaco Canyon, Casa Rinconada (noted for its many astronomical alignments) to AD
1054.

Now, it’s true that there is a single tree-ring cutting date from Casa Rinconada that dates to 1054.  This is, however, the only tree-ring date for the site, so while it’s plausible that it dates the construction of the site this definitely cannot be stated as definitively as Pauketat and Emerson state it here.  There is no specific provenience information available for this beam, so there’s no way to tell how it was used and whether it can plausibly be said to date to the initial construction of the site.  The general architecture of Casa Rinconada is consistent with a construction date in the 1050s, but without more specific information tying it to a specific year on the basis of one unprovenienced beam is unwarranted.

Looking through Solstice-Aligned Opening at Casa Rinconada toward Aligned Niche

Furthermore, even if Rinconada was built in 1054, that doesn’t establish that it was built because of the supernova.  There was extensive construction in the canyon throughout the mid-1000s, associated with Chaco’s apparent rise to regional dominance, and this began well before 1054.  The major expansion of Pueblo Bonito began by the 1040s at the latest, and various other construction projects at other sites in the canyon dates to this general period.  Rinconada could easily have been part of this general process without any specific relationship to the supernova.  Indeed, there’s nothing about Rinconada that seems to refer to the supernova, despite the various astronomical alignments (some of them controversial as well, it should be noted) identified there.

None of this means that the supernova didn’t have an important role at Cahokia, of course, and it doesn’t even rule out an important role at Chaco itself.  It does mean, however, that developments at Chaco shouldn’t really be used as evidence for developments at Cahokia, even though the two sites are contemporaneous and Chaco can be dated much more precisely.  Cahokia may well have risen as a result of the 1054 supernova, but neither the Supernova Petroglyph at Chaco nor the one tree-ring date at Casa Rinconada provides evidence that it did.
ResearchBlogging.org
Pauketat, T., & Emerson, T. (2008). Star Performances and Cosmic Clutter Cambridge Archaeological Journal, 18 (1), 78-85 DOI: 10.1017/S0959774308000085

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