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Archive for the ‘Geology’ Category

Ledge at Wukoki Pueblo, Wupatki National Monument

Wupatki is a very dry place even by the standards of the Southwest, with annual precipitation averaging about 8 inches.  Human habitation in such an arid landscape is therefore highly dependent on capturing as much available moisture as possible.  It appears that the prehistoric inhabitants took advantage of the volcanic ash laid down over the area by the eruption of Sunset Crater in AD 1064 for farming purposes since it acted as a mulch, retaining water from the summer rains that would otherwise have evaporated in the heat and strong winds.  For other purposes such as drinking, cooking, and construction, however, water trapped in the soil isn’t very useful, so other sources needed to be found.  As at Chaco Canyon, which is similarly dry, some of this water would have come from a few springs in the area, especially in the dry season, but it would also have been useful to capture as much of the runoff from the summer rains as possible.  Due to the geology of the Wupatki area, this water could only be used for floodwater farming in a very few places, but there were other ways to take advantage of it.

One such way was apparently shown by a discovery made by two National Park Service archaeologists in the 1940s.  While out evaluating sites for stabilization needs, Albert Schroeder and Philip Van Cleave found some potsherds on the ground in sufficient number to make them think that they might be reconstructible into something approaching the original vessel.  They picked up the sherds and dug a bit into the ground beneath them to see if there were any more.  Sure enough, just under the surface of the ground there was a whole ring of sherds in place, indicating the presence of a broken but substantially complete jar that had apparently been deliberately buried.  They excavated it and took some pictures, and Schroeder wrote up a short article on the discovery for American Antiquity which was published in 1944.

Small Site on Ledge, Box Canyon, Wupatki National Monument

The jar was of the ceramic type Moenkopi Corrugated, which Schroeder dates to AD 1075 to 1275.  This is unfortunately a quite wide date range, encompassing almost the entire period of substantial prehistoric occupation of Wupatki, so it is not possible to say at what point during the occupation the jar was buried.  From its position, however, Schroeder was able to determine that it was likely placed to capture runoff from the summer rains.  It was buried in the sand underneath one of the sandstone ledges that are so common at Wupatki, so one possibility is that it was placed to capture runoff from the ledge.  Indeed, it seemed that the part of the ledge above the jar naturally collected runoff from a wide area of the sandstone outcrop.  At the time Schroeder and Van Cleave found the jar, however, the water pouring off the ledge fell somewhat short of where the jar was.  Schroeder suggested that there may have been some erosion in the period between the time the jar was buried and the time it was found, such that at this time of placement the ledge extended further out and the runoff may have poured directly onto the jar.  If this was not the case, however, the jar was probably buried with the sand level with or a bit higher than the rim, so that runoff from the sandy ground around the jar rather than the ledge above would flow into the jar.

Either way, it seemed apparent to Schroeder that the purpose of the jar was likely to collect water, which makes sense in such an arid environment.  He admitted to being somewhat unsure of the details of his proposal, and he did not venture any theories as to what the water would have been used for or why a jar was used in this way to collect it.  Obviously the amount of water in a single jar would not have been much for agricultural purposes, so I suspect the water was used for household use.  To be so used, depending on how close the household in question was (which Schroeder unfortunately did not mention), the jar could either have been dug up after filling or left in place.  In the latter case, the water could have been taken out with a ladle and transferred to a canteen or some other sort of vessel for transportation.

I don’t have any sort of major point to make about this paper, but it’s interesting as an example of the kinds of adaptations people make to harsh environments.  Wupatki would have been a hard place to live in prehistoric times, but people gave it their best shot.
ResearchBlogging.org
Schroeder, A. (1944). A Prehistoric Method of Collecting Water American Antiquity, 9 (3) DOI: 10.2307/275790

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T-Shaped Doorway at Lomaki, Wupatki National Monument

The paper by Glenn Davis Stone and Christian Downum that I mentioned in the last post, which evaluated the archaeological record of the Wupatki area of northern Arizona in the light of Ester Boserup‘s theory of agricultural intensification, was based largely on the data from an extensive archaeological survey of Wupatki National Monument done by the National Park Service in the 1980s.  This data is presented in a more complete form in an earlier paper that Downum cowrote with Alan Sullivan.  This paper looks at the previous models proposed for the settlement and abandonment of Wupatki in the context of the new data from the survey.

Cinder Cones from the Citadel, Wupatki National Monument

The most influential model for the prehistory of Wupatki has been that presented by Harold Colton of the Museum of Northern Arizona based on work done in the 1930s and 1940s.  Colton saw the extreme aridity of Wupatki as having discouraged settlement there until the eruption of Sunset Crater Volcano in AD 1064 spread a layer of volcanic ash over the area.  This ash acted as a natural mulch to retain water from the infrequent rains which would otherwise evaporate from the thin soil.  Colton looked at the large number of sites that seemed to have been built in the aftermath of the eruption and saw a “land rush” in which people from all over the local area come to Wupatki to take advantage of the improved conditions for farming from the ash fall.  Over time, however, the ash cinders began to blow away in the strong winds and the productivity of the land declined, so the people began to aggregate into the large pueblos for which the Wupatki area is best known.  Once in these aggregated villages, the poor sanitary conditions of living in such close quarters, combined with the continuing decline of agricultural conditions, forced the abandonment of the whole area some time in the thirteenth century.

Wall Abutment, Wupatki Pueblo

This is a plausible story on the face of it, but Colton’s account has been challenged more recently by other archaeologists who point out that a great many of the structures built soon after the ash fall that Colton included in calculating the population increase were small, ephemeral structures that probably served as field houses or other special-use locations rather than year-round dwellings.  This implies that Colton was double-counting both these impermanent structures and the actual permanent houses of the people who used them, thus coming up with inflated population figures on which he based his “land rush.”  The systematic nature of the survey in the 1980s provided the opportunity to determine just how many sites there really were and how many actually served as permanent dwellings.

The Citadel and Sunset Crater from Lomaki, Wupatki National Monument

As Downum and Sullivan tell it, the results basically vindicate Colton’s critics.  The vast majority of the structures found were small and relatively impermanent, with few artifacts.  In addition, a careful tabulation of sherd types at most of the sites showed that the immediate post-eruption period, far from being the land rush of Colton’s theory, was actually a time of relatively limited occupation.  There were more sites from this period than from the pre-eruption period, when the area was nearly uninhabited, but still not very many.  It was not until a few decades later, starting around AD 1130, that building began to really pick up, as indicated by both sherd types and tree-ring dates.  The high point of construction didn’t come until the 1160s, a century after the initial eruption.  (It is actually not clear how long the eruptions continued after the beginning around 1064, and there may well still have been occasional activity by the volcano this late or even later.)  Construction seems to have effectively ceased by 1220, and the area was probably abandoned not long after that.

Beam Sampled for Tree-Ring Dating, Wupatki Pueblo

The upshot of all this for Colton’s theory is that, while it does seem to be true that the ash improved the suitability of Wupatki for agriculture, people didn’t immediate act to take advantage of this.  Downum and Sullivan propose that this may have been because it took some time for the effects of the ash fall on the soil to manifest, but I think a more plausible explanation for this can be found by looking outside the immediate area to the larger region.  The decades after 1130 were a time of extensive drought throughout the northern Southwest.  This is when Chaco collapsed (or at least declined), and there were likely extensive migrations all around the region.  In this context, people may have come to Wupatki less from the “pull” factor of the beneficial effects of the volcanic ash and more from the “push” factors of drought and/or political instability elsewhere.  Of course, there were at least some people farming at Wupatki before this, so the fertility of the area may have become well known at the same time as things were deteriorating elsewhere, making both push and pull factors part of the regional dynamics.

Great Kiva at Wupatki Pueblo

In line with the arguments in the later paper by Downum and Stone, Downum and Sullivan here argue that agriculture for most of the period of occupation of Wupatki was extensive rather than intensive.  They do claim, however, that intensification came right at the end of the occupation period, after 1220, on the basis of more intensive usage of the sites from that period based on sherd counts.  This is kind of dubious, and it appears that Downum changed  his mind about it in the eight years between this paper and the later one.  Intensification at this can, however, be incorporated into the argument made in the later paper that intensification was impossible in this area due to ecological conditions.  Once people began to leave the area, perhaps spurred by increased warfare and/or continuing climatic instability, those who remained would not necessarily have been able to secure access to the large amounts of land they had had claimed earlier as part of the consolidated political groups associated with the large pueblos in the Stone and Downum model.  These few remaining farmers may then have attempted to intensify production on the smaller amounts of land available to them.  Given the aridity of the area, however, this would not have worked reliably enough to allow them to stay, so within a few decades or less they would leave as well, leaving the entire Wupatki area abandoned by 1275.  Note that this is when the famous “Great Drought” associated with the abandonment of Mesa Verde and other areas began, so the aggregation and abandonment processes associated with Wupatki may well have been different from the similar processes elsewhere in the Southwest.

Upper Walls Built on Rock Outcrop, Wupatki Pueblo

Since I’ve been taking note of the scholarly context of the papers I’ve been discussing lately, I should point out that this one is very much an archaeology paper, and a classic processual one at that, with lots of statistics and an explicit model of interactions between people and the environment.  This certainly makes it more “scientific” than, say, the later paper by Downum and Stone, which is more anthropological and not very scientific at all, but as with many such archaeological papers the scientific trappings are somewhat superficial.  This is definitely not as rigorous an attempt at quantitative social science as the economics paper on plowing and gender roles I discussed a little while ago, for instance.  I would therefore argue that this is only science in a somewhat questionable expansive sense, and not necessarily anthropology at all, despite the frequent claims of processualists to be doing “archaeology as anthropology.”  Again, however, that doesn’t mean it’s not worthwhile scholarship.  Regardless of how it’s classified, this is interesting research that can serve as a useful source of data for a variety of other studies such as the one Downum later did with Stone.
ResearchBlogging.org
Sullivan, A., & Downum, C. (1991). Aridity, activity, and volcanic ash agriculture: A study of short-term prehistoric cultural-ecological dynamics World Archaeology, 22 (3), 271-287 DOI: 10.1080/00438243.1991.9980146

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Wupatki Pueblo

The paper I discussed earlier on the connection between plow-based agriculture and highly inegalitarian gender roles was based on a theory proposed by Ester Boserup.  Boserup was a Danish economist who had a lot of interesting ideas about the relationship between population growth and agricultural intensification.  She’s best known for arguing that intensification of agricultural production is a response to population growth, rather than a cause of it as Malthus proposed.  The basic idea is that the default mode of agricultural production is extensive, i.e., requiring a lot of land but relatively little labor.  As population grows, however, the amount of land available per person declines, so people need to get more production out of each unit of land.  This generally requires more work, and the amount of production per unit of work declines.  That is, although the overall amount of food produced increases, the amount of food produced for the amount of work expended to grow it declines.  Thus, people will only intensify agricultural production when they are forced to do so by increasing population.

The Citadel at Wupatki National Monument

This model has been very influential, but it has also been criticized on a number of fronts.  Many of these relate to the underlying assumptions, which Boserup didn’t really make explicit.  The model assumes that the amount of land available is fixed, and doesn’t make allowances for other responses to increased population growth such as trade, migration, and conquest.  There have also been a number of cases in which the model doesn’t seem to apply, either because increased intensification does not in fact require more work or because putting more work into intensified agriculture does not in fact increase crop yields.  (Note that these objections come largely from cultural anthropologists based on ethnographic data.)

Rooms at Wupatki Pueblo

A 1999 paper by Glenn Davis Stone and Christian Downum (available here) tries to incorporate the criticisms of Boserup’s model into a recasting of the model that sees it as applicable only under certain circumstances, namely where increased labor is both necessary and sufficient to raise production.  When this is the case, one option for coping with increased population pressure is what they term “Boserupian intensification,” which is basically the process Boserup described in which people work harder and get higher total yields but lower yields per unit of work on a fixed amount of land.  There are other options, however, including migration and trade, for dealing with population growth in this context, and in other contexts where Boserupian intensification is not an option because of ecological conditions those other options comprise the whole set of possible responses.  In conditions where intensification is possible without harder work, due to new technology or innovative techniques, population pressure ends up not being much of a problem.  Examples given in the paper include raised-field agriculture in the Andes and rice paddies in East Asia.  In other conditions, however, such as arid environments where the weather is very unpredictable, intensification through increased labor just doesn’t work to increase yields reliably, and population pressure becomes a very big problem that must be addressed through other solutions.

Entrance Sign, Wupatki National Monument

Stone and Downum illustrate their proposal through an examination of Wupatki.  This is a very arid part of northern Arizona with similar climatic conditions to Chaco Canyon.  Like Chaco, it was also (rather mysteriously) a major population center in prehistoric times.  Wupatki’s heyday came mainly in the twelfth and early thirteenth centuries AD, a little later than Chaco’s in the eleventh and early twelfth.  Many years ago Harold Colton of the Museum of Northern Arizona proposed that the rise of Wupatki was a response to the eruption of Sunset Crater Volcano in 1064, which covered the area with volcanic ash that served as a natural mulch and greatly increased local fertility, leading to a massive influx of population.  This theory has been challenged more recently but it seems to still have a large number of adherents, and Stone and Downum seem to be among them.  They take the idea of increased fertility from the volcanic ash for granted and look at what happened once people started to move into the Wupatki area.  There have been proposals that the increased population pressure from immigration led to intensification of agriculture at Wupatki in a classic example of Boserupian intensification, but Stone and Downum look carefully at the evidence and conclude that there is very little evidence of any intensification.  Instead, they argue that the vast majority of the Wupatki area is totally unsuitable for intensification; there are very few places where any kind of irrigation or floodwater farming can be practiced, and for the most part the only way to grow anything is to extensively dry-farm the open spaces.  Thus, intensification was not an option, and other options for dealing with population pressure must have been pursued.

Dry Land Farming Sign at Box Canyon, Wupatki National Monument

The strategy they see as most likely is political consolidation to secure claims to land.  Since the necessity of extensive agriculture made holding on to as much land as possible a necessity, coming up with effective means of demonstrating and enforcing land rights was a high priority.  They see the most likely way this would have happened is the formation of political units organized along ethnic lines.  It is always difficult to recognize ethnicity in the archaeological record, but Wupatki has long been known as a “frontier” area occupied by people of three distinct archaeological “cultures”: Kayenta Anasazi, Sinagua, and Cohonina.  These presumably don’t correspond exactly to “ethnicities” in the modern sense, but there are notable differences in material culture among the three, and Stone and Downum identify two main clusters of settlements including large, impressive pueblos.  One of these, centered on Wupatki Pueblo, seems to show Sinagua affiliations, while the other, centered on the Citadel, shows more Cohonina affiliations.  The place of the Kayenta Anasazi in all this is unclear.  They don’t seem to have a cluster of their own, and Kayenta-affiliated sites are spread all over the area.

Wall at the Citadel, Wupatki National Monument

Stone and Downum see the construction of large, aggregated pueblos as a sign of group power intended to impress others with the legitimacy of the group’s claims to land and other resources, and they suggest that relatively few people might have actually lived in the pueblos themselves despite being affiliated with them politically.  For this system to work, the groups’ land claims had to be backed with the credible threat of coercive force, and there is indeed some evidence of violence at Wupatki that may reflect occasional instances when this force needed to be shown.  (There is an interesting parallel here to a more recent article on a different part of the Southwest which I will discuss at some point.)

Wall at Wupatki Pueblo

To illustrate the plausibility of their interpretation of Wupatki, Stone and Downum rely on analogy to contemporary ethnic groups in central Nigeria.  This is an area where Boserupian intensification is in fact possible and some groups have dealt with population pressure through intensification.  Other groups, however, have responded instead by organizing along ethnic lines to defend their land claims through the threat and occasional application of violence.  Stone is a sociocultural anthropologist and this part of the paper is based on his fieldwork in the area.  This is a good example of what (sociocultural) anthropology can contribute to interdisciplinary scholarship.  Ethnography produces an enormously rich, textured body of qualitative data that can be used to test hypotheses and models to explain social phenomena.  Those models can come from anthropology itself, of course, but they can also come from other disciplines, such as economics in this case.  Downum is a Southwestern archaeologist, and his role in this paper seems to be in providing the data about Wupatki.  Much of the data comes from an extensive survey of sites within Wupatki National Monument which has greatly increased the amount of information available about this interesting but poorly understood area.

San Francisco Peaks from Wukoki Pueblo, Wupatki National Monument

I think the arguments in this paper are pretty plausible.  There are some questions about the application of the theory to Wupatki, but it seems to fit as well as any other explanation I’ve seen for the processes of aggregation and abandonment that marked this period of Southwestern prehistory.  The basic idea is that aggregation occurred because of political consolidation, which came about to secure land claims in the face of population pressure and inability to intensify production.  Along with this consolidation came increased conflict, and ultimately that conflict and poor climatic conditions led to abandonment.  This is similar to the model I have proposed for the role of warfare in spurring aggregation and abandonment, although there I focused more on warfare specifically as a response to resource scarcity rather than political consolidation as the response and warfare as the result of that.  This is really a difference of emphasis, however, and the basic idea is very similar.  What Stone and Downum’s theory doesn’t explain, however, is the widespread nature of the aggregation and abandonment processes across the northern Southwest, even in places with much better ecological conditions such as Mesa Verde where intensification would presumably have been an option in a way it wasn’t at Wupatki.  They acknowledge this, and make no claim to explain anything beyond the specific local situation, but it’s an issue that is worth thinking about in evaluating theories like this.

Interior Room at Wupatki Pueblo

Since I’ve been talking a lot lately about disciplinary issues in academia, it’s worth noting that this paper seems to be to be pretty much entirely a cultural anthropology paper.  It uses archaeological data, and one of the authors is an archaeologist, but the overall analysis lies squarely within the realm of (sociocultural) anthropology.  It’s well-done, too, and quite serious and empirical.  I suspect its authors are probably among those who consider themselves “scientific anthropologists” and are outraged by the American Anthropological Association’s moves toward removing “science” from the definition of the field.  I wouldn’t call this science, though.  There’s no hypothesis testing or statistical analysis, and the analysis is basically comparative and qualitative.  It doesn’t go so far in that direction as historical papers like Robin Ganev’s, which I discussed in the previous post, but it’s nowhere near as scientific as the economics paper on plowing that I discussed in the post before that.  What I take from this is that scholarship doesn’t need to be scientific to be serious.  Indeed, in a paper like this one of the main advantages is to take a more “scientific” theory like Boserup’s and evaluate it from a more qualitative perspective to define the unstated assumptions behind it and the conditions under which it applies.  I still maintain that anthropology is not a science, but that doesn’t mean it isn’t worthwhile or doesn’t count as serious scholarship.
ResearchBlogging.org
Stone, G., & Downum, C. (1999). Non-Boserupian Ecology and Agricultural Risk: Ethnic Politics and Land Control in the Arid Southwest American Anthropologist, 101 (1), 113-128 DOI: 10.1525/aa.1999.101.1.113

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Close View of Sunset Crater Volcano

Most research on human-environment interactions focuses on large-scale changes in environmental conditions over long periods of time (by human standards, at least).  There are good reasons for this, especially when applied to prehistory, most importantly that there are a lot of potential data sources for environmental conditions that can be correlated with cultural chronologies to identify possible relationships between the two.  A lot of research in the Southwest along these lines has sought to correlate periods of higher and lower average rainfall, readily apparent in tree-ring records, with population increases, decreases, and movements, as inferred from the number and types of archaeological sites in a given area, which conveniently can be dated with those very same tree-ring chronologies.  Jeff Dean at the University of Arizona’s Laboratory of Tree-Ring Research has been a major figure in this sort of research for a long time, and it’s resulted in a lot of interesting insights and theories about Southwestern prehistory.

"Squeeze-Up" at Sunset Crater National Monument

As we’re seeing right now in Iceland, however, there is another type of environmental event that can affect human societies: a short, intense, unexpected, and uncontrollable catastrophe like an earthquake or a volcanic eruption.  These are generally harder to see in the paleoclimatological record, and as a result they are hard to correlate with cultural changes.  Volcanoes themselves, however, are an exception to this invisibility, since they spew out all kinds of ash and lava that have very visible effects on the local geology.  In many cases these can be dated by radiocarbon or other methods and correlated with events in the societies of the people living in the area.  One very good example of this is found in Alaska among the northern Athapaskans.  Another is closer to home, as it were, from the perspective of this blog: Sunset Crater.

Sign Explaining "Squeeze-Up" at Sunset Crater National Monument

Sunset Crater is northeast of Flagstaff, Arizona.  It is the most recent of the San Francisco Peaks to erupt, and the only one to erupt during the time that humans have occupied the area.  It erupted sometime in the mid-to-late eleventh century AD; the date 1064 AD gets thrown around a lot, based on some tree-ring samples at Wupatki that showed odd ring patterns in the few years after that, but this dating has been questioned and the general consensus is only that the eruption occurred sometime around this time, based on the (often quite large) deposits of ash found in sites from this period.  Note that this is during the height of the Chacoan era.  The eruption may have been visible at Chaco itself, and it was certainly visible at some of the outlying Chacoan sites, so the Chacoans, along with everyone else in the region, would definitely have been aware of the events even though the immediate area shows little to no Chacoan influence.  It’s not clear how long the eruption lasted.  Eruptions of cinder cone volcanoes can potentially go on intermittently for decades, although they can also be much shorter.  Sunset Crater could have kept erupting for as long as 100 years or even 200, but more data are needed to determine this more precisely.

Sandstone and Igneous Masonry at Nalakihu, Wupatki National Monument

One theory about the effect of the eruption on human societies, first formulated by Harold Colton of the Museum of Northern Arizona in the 1930s, is that while the initial eruption was devastating to the small local population, the layer of ash that the eruption laid down turned out to be an excellent mulch, holding in much-needed moisture in this dry area and making agriculture much more productive, which spurred a massive influx of population to places like Wupatki that had been covered by ash and led to substantial cultural changes.  This theory has since been challenged, and there is no real consensus today on what effect the eruption had on cultural dynamics in the area.  It is highly unlikely, however, that it had no effect.  A volcanic eruption is a big disruption to existing patterns of living.

Lava at Valley of Fires Recreation Area, Carrizozo, New Mexico

One interesting and concrete manifestation of the effects the eruption may have had on local people comes from an interesting paper (which is my source for most of the general information about Sunset Crater above) on some building stones found at a nearby habitation site that show clear imprints of corncobs in them.  The authors conclude that this could pretty much only result from people deliberately going to places where lava was coming out, probably small features known as hornitos that would have been easily approachable, and putting in offerings of corn cobs to let the lava run over them, then after the lava cooled taking the rocks back to the site (which is a few miles away) and forming them into building blocks with distinct corncob impressions.  This would have been a lot of work, so it’s pretty apparent that it had a lot of cultural importance in some way.

Post Office, Carrizozo, New Mexico

Another interesting cultural connection to volcanoes is suggested in this article in the Alamogordo Daily News (via Southwestern Archaeology Today) about a salvage archaeology project south of Carrizozo, New Mexico, an area of considerable volcanic activity, that uncovered a large site that seems to probably date to around AD 900 to 1100, again during the Chacoan period.  This era is not very well-understood in this part of New Mexico, which was occupied by the Jornada Mogollon who may have later played an important role in the origins of the kachina cult.  One of the crew members, a woman from Santa Clara Pueblo, mentions that “where the lava comes out … represents the underworld.”  The article is kind of confusingly written, so it’s not clear exactly what she means by that, but it’s a really interesting clue to the importance of volcanoes to Pueblo people.  I don’t know much about the dating of the lava flows around Carrizozo, so I don’t know if the Jornada Mogollon would have been around to see the actual lava come out, but even if they didn’t they may have regarded certain vents and other features with reverence.  They certainly used the resulting igneous boulders as a medium for their extensive and innovative petroglyphs.

Carrizozo Trading Company Sign, Carrizozo, New Mexico

I’m increasingly coming to think that the importance of sudden, catastrophic events like volcanic eruptions has received too little attention among archaeologists.  Certainly long-term climatic changes are important, as are culture, political, and historical factors, but a catastrophe has a way of forcing changes very suddenly that may shed light on some of the more puzzling changes in the archaeological record.  Something to think about as we watch the effects of a volcano in Iceland on people throughout northern Europe and beyond.
ResearchBlogging.org
Elson, M., Ort, M., Hesse, S., & Duffield, W. (2002). Lava, Corn, and Ritual in the Northern Southwest American Antiquity, 67 (1) DOI: 10.2307/2694881

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Sunset Crater Volcano

I’ve written a lot here recently about the Athapaskan migration(s) into the Southwest.  It’s a very interesting topic in a lot of ways.  I find it especially fascinating because although the evidence that it happened is very strong, nothing else about it can be easily determined.  We know that at least one migration of Athapaskan-speakers from northern Canada to the Southwest happened, but we don’t know when it happened, what route it took, or why the Athapaskans left the north in the first place.  Archaeology, linguistics, and ethnography all contribute some clues to this puzzle, but there’s so much ambiguity remaining that the mystery is by no means anywhere near solved.

"Birth of a Mountain" Sign at Sunset Crater

In addressing the “why” question specifically, it is perhaps most fruitful to look at the starting point rather than the ending point.  Although archaeological evidence for Athapaskan groups in Alaska and Canada doesn’t seem to appear until the early centuries AD, and even then it’s not necessarily entirely clear who those people are, this is much more evidence for Athapaskan presence in a particular place at a particular time than anything in the Southwest until historic times, and infinitely more evidence than anything anywhere in between.  Looking at the north also has the advantage of the continuing presence of a wide variety of Athapaskan groups, and their linguistic relationships and oral traditions are potentially useful evidence in understanding their past, and by extension the past of the people who once lived among them but later went south.

Bridge at Sunset Crater

A fascinating paper from 1992, though not focused specifically on the migration of the Southwestern Athapaskans, contributes considerably to this issue.  The starting point is oral traditions among some, but not all, of the northern Athapaskans describing phenomena at the beginning of time that sound very much like the events surrounding the eruption of a volcano.  This isn’t very surprising, since Alaska is an area with considerable volcanism, but it’s important to note that even in volcanically active areas volcanoes don’t actually erupt very often.  Indeed, intervals between eruptions are routinely measured in centuries or even millennia.  Since human generations are so much shorter, knowledge of volcanic eruptions in oral history, even if, as is usually the case, it’s in a very heavily mythologized and allegorical form, in most cases probably results from direct experience of specific eruptions that can be dated geologically and correlated with the human occupation of the area.  A well-known Southwestern example is the eruption of Sunset Crater near Flagstaff, Arizona in the late eleventh century AD.  This event remains well-remembered in Hopi traditions, and it has also played a considerable role in the development of archaeological ideas about the Sinagua people who inhabited the area prehistorically.

Sunset Crater Visitor Center

Turning back to the northern Athapaskans, the only volcano to have erupted in the (rather extensive) areas they have traditionally occupied in the relatively recent past is Mt. Churchill, in eastern Alaska very close to the border with the Yukon Territory.  There appear to have been two major eruptions of this volcano: one around AD 20, which resulted in a major area mostly to the north being covered in volcanic ash, and another much larger one around AD 720 which resulted in a very large area to the east being covered with a thick layer of ash.  If, as seems probable, Athapaskan-speaking people were living in the area when these eruptions occurred, they would surely have made a profound impact on their lifestyles.  Indeed, either or both of them could have made such large areas uninhabitable that the people who had been living there migrated elsewhere.  And that, of course, is where the relevance of all this to the Southwestern Athapaskans comes in.

"Volcanoes All Around You" Sign at Sunset Crater

So, assuming the oral traditions of the northern Athapaskans record a memory of an actual volcanic eruption, which one was it?  The authors of the article conclude that it was most likely the AD 720 eruption.  For one thing, this is the more recent one, and it would be more likely to be remembered simply on that basis.  It was also more powerful than the earlier eruption, which would also make it more memorable.  Indeed, it was a very powerful eruption.  It had a Volcanic Explosivity Index of 6, the same as Krakatoa and Mt. Pinatubo.

San Francisco Peaks from Sunset Crater

There’s also the matter of which specific groups have the traditions in question.  It turns out that the volcano traditions are not present among all northern Athapaskan groups, but are highly localized among the peoples of the Mackenzie River region of the Northwest Territories, due east of Mt. Churchill and the ash fall from the AD 720 eruption.  Some of these peoples have traditions mentioning a mountain that exploded in fire, while others mention conditions that sound like the ash fall and the subsequent period of cold weather.  There are also references to the discovery of copper, which occurs in elemental form in the general area and may have been dislodged by the eruption, around this same time, and some of the stories even link the copper directly to a fiery mountain.  In historic times the people who lived in the area of Mt. Churchill controlled a substantial amount of the trade in native copper, which only occurs in a few parts of North America.  These groups, however, although they do speak Athapaskan languages, apparently do not have any traditions referring to a volcanic eruption, which suggests that they were living elsewhere at the time and only moved into the area after it had recovered ecologically from the effects of the ash fall.  Similarly, a recent study has suggested that the caribou populations in the area today are not related either to surrounding populations or to the caribou that lived in the area before the eruption, suggesting that it was uninhabitable for caribou for some period after the ash fall.

"Life and Landscape Transformed" Sign at Sunset Crater

Thus, the article concludes that it is very likely that the AD 720 eruption made the area uninhabitable and so traumatized the inhabitants that they moved to the east, past the mountains into the Mackenzie River valley, to become the various peoples that the article refers to collectively as the “Dene” (something of a confusing term, since most of the Athapaskan-speaking groups call themselves by a cognate of this term, such as Navajo Diné).  The traditions also refer to a divergence of languages after the time of the eruption, before which all the people could understand each other.  This is certainly intriguing, since this is apparently what did happen, but it’s important to note the similarity to the Tower of Babel story here.  These stories were recorded by a Christian missionary who spent many years in the area, and the people he ministered to would certainly have been familiar with the Babel story and may have incorporated parts of it into their own traditional stories.  Nevertheless, they may have done so specifically because the story of the eruption already involved a divergence of languages.  There is, of course, no volcano in the story of the Tower of Babel, so there’s something more going on here than a straight adaptation of a biblical story to a native context.

Cinder Hills Overlook Sign at Sunset Crater

The connection to the Southwestern migration is somewhat subtle.  Since the Navajos and Apaches don’t have anything like these volcano traditions, it doesn’t seem likely that the eruption forced people to migrate all the way across the continent.  Rather, it’s more likely that the migrating Dene from the ash-fall zone entered territory previously occupied by other Athapaskan groups and set off a chain reaction of migrations that eventually led to the Pacific coast and the Southwest.  The details and dates remain vague, of course, and will continue to do so until the elusive archaeological evidence for the migration itself appears.  If the eruption was the ultimate cause, however, it does set a terminus post quem for the migration, which couldn’t have happened earlier than AD 720 and probably would have been some time later, after the early parts of the chain of population movements had occurred.  Note that this doesn’t say anything in particular about when the Athapaskans arrived in the Southwest; pretty much all dates that have been posited so far would work with this scenario.  Nor does it give much insight into the route the migration would have taken, which depends on who was living where and which way they went after being pushed out.

Lava at Sunset Crater

All of this evidence points to the era after the breakup of Proto-Athapaskan as the time of the eruption, which makes sense for other reasons as well.  The most divergent Athapaskan languages (i.e., the ones likely to have broken off earliest) are to the west, further into Alaska, and they don’t have any volcano traditions.  Nevertheless, and more speculatively, the authors suggest that the earlier, smaller eruption of Mt. Churchill might have played a role in the initial breakup of the protolanguage, despite not being impressive enough to be remembered.  If the protolanguage was spoken in the area around the volcano, which some have suggested on other grounds, then even a small eruption could have sent some groups away early, resulting in the striking diversity of northern Athapaskan language groups.  Some of those people might even have come back and resettled the Mt. Churchill area after the AD 720 eruption.  Again, though, this is all speculation without much evidence behind it.

"Power to Symbolize" Sign at Sunset Crater

Overall, I think this is a fascinating subject.  The interaction between people and the environment gets a lot of attention these days, but it’s mostly in the context of people’s effects on the environment.  Sometimes, however, the environment gets to call the shots, and it does so in the form of flaming mountains and showers of ash.  People just have to deal with it the best they can.
ResearchBlogging.org
Moodie, D., Catchpole, A., & Abel, K. (1992). Northern Athapaskan Oral Traditions and the White River Volcano Ethnohistory, 39 (2) DOI: 10.2307/482391

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Turquoise-Covered Pottery, Santa Fe, New Mexico

Probably no single material is more closely associated with Chaco than turquoise.  The vast amounts found in Room 33 at Pueblo Bonito alone suggest its importance, but it has been found in considerable quantities at many different sites, both small houses and great houses and both inside and outside of the canyon.  There is considerable evidence that manufacture of turquoise jewelry became a major activity in Chaco and some of the outlier communities during the period when the Chacoan system was beginning to form, and probable ornament manufacturing areas have been found at both great houses and small houses.  It’s not clear what precise role turquoise may have played in the system (though there are some intriguing possibilities suggested by other lines of evidence), but it is apparent that it was an important one.  It’s also important to note that unlike some rare artifacts, such as shell trumpets, turquoise seems to have been associated with the system as a whole rather than with Chaco Canyon or Pueblo Bonito specifically.  Both finished artifacts and manufacturing debris are found in significant quantities at many outliers, especially to the south in the Red Mesa Valley.

Turquoise Display at Visitor Center Museum

What’s really remarkable about this apparent centrality of turquoise is that there are no turquoise deposits anywhere near Chaco, or indeed within the area covered by the Chaco system as a whole.  All of this turquoise had to be imported from somewhere, and this importation was clearly occurring on a vast scale and over a relatively long period of time.  The closest source of turquoise to Chaco is in the Cerrillos Hills south of Santa Fe, which have extensive turquoise deposits that show much evidence of being mined in antiquity (as well as in modern times), including some apparent campsites with material culture suggestive of a connection to the San Juan Basin.  For a long time most researchers assumed that most or all of the turquoise at Chaco came from Cerrillos, and for a while it was fashionable to come up with theories explaining the rise of Chaco as being based on control of the Cerrillos mines and the trade routes connecting them with the vast market for turquoise in Mesoamerica.  These theories have more recently fallen out of favor for a number of reasons, one being the general trend away from emphasizing Mesoamerican influence on the Chaco system and another being the inconvenient fact that many of the most productive turquoise deposits in the Southwest are in southern Arizona and New Mexico, considerably closer to Mexico than Chaco, which makes it difficult to explain how the  Chacoans could have sustained a monopoly on the turquoise trade.

Turquoise Display at Chaco Museum

This whole issue would benefit greatly from more precise information on the actual source of Chaco’s turquoise.  The idea that it came from Cerrillos is basically just an assumption based on geographical proximity, and while it’s a reasonable enough assumption there have been many attempts to use chemical properties of the turquoise to determine its precise origin and either confirm or deny the Cerrillos hypothesis.  Most of the early attempts to do this using trace element analysis were unsuccessful, due mainly to the complicated internal structure of turquoise as a material.  One recent  paper, however, reports on a remarkably successful attempt to use a new technique based on isotope ratios to characterize sources and assign artifacts to them.  The technique uses two isotope ratios: hydrogen to deuterium and copper-63 to copper-65.  The combination of the two ratios can be used to define a two-dimensional space within which individual samples can be placed to determine if samples from the same source cluster together.

Anthill at Pueblo Bonito with Piece of Turquoise

It turns out they do.  The researchers used samples from a variety of Southwestern turquoise sources, most of which show clear evidence of having been used in antiquity, including three in the Cerrillos area, one in southern New Mexico, two each in Colorado and Arizona, and four in Nevada.  They analyzed several samples from one of the Arizona mines to test internal variation within a single source.  There turned out to be little variation, suggesting that individual sources generally have homogeneous isotope ratios, and the three Cerrillos sources also clustered close to each other, suggesting that this similarity in ratios operates at a regional as well as local scale.

Sign at Santuario de Guadalupe, Santa Fe, New Mexico

The researchers also tested several pieces of turquoise found at several small houses in Chaco Canyon and one at the Guadalupe outlier community, which marks the far eastern edge of the Chacoan system and is the closest Chacoan community to Cerrillos.  Guadalupe plays a key role in models of Chaco that posit Chacoan control of the Cerrillos mines, since any transport of turquoise from Cerrillos to Chaco would almost certainly have to have involved Guadalupe as an intermediate stop.  Guadalupe is thus probably the outlying community most relevant to an investigation of Chacoan turquoise sources.

Santuario de Guadalupe, Santa Fe, New Mexico

The results were interesting.  Several of the artifacts seem to have come from Cerrillos, with a much higher proportion at Guadalupe than at Chaco, but a few other sources were present as well, including one of the Colorado sources at Guadalupe and the southern New Mexico source and two Nevada sources at Chaco.  Four artifacts matched none of the sources tested, implying that they came from some other, as yet unidentified, source.  The Chaco artifacts came from a wide range of chronological contexts, with earlier periods more strongly represented than later ones.  The Guadalupe artifacts unfortunately didn’t come from a securely dated context, so nothing much can be said about their relative or absolute chronology.  In general, the Chaco artifacts seem to have come from a wide range of sources in all time periods, but the sample size is so small that it is hard to come to any more specific conclusions.

Turquoise-Encrusted Cow Skull, Santa Fe, New Mexico

This paper is really just a pilot project, intended primarily to demonstrate the methodology used, and the conclusion mentions that continued research using more sources and artifacts is underway.  The main conclusion that can be drawn at this point is that assuming all the Chaco turquoise came from Cerrillos is no longer warranted, and it seems the trade networks in the prehistoric Southwest were much more elaborate and far-flung, at least for valuable, portable materials like turquoise, than such an assumption would suggest.  Chaco may or may not have been primarily about turquoise, but it certainly wasn’t about Cerrillos turquoise.
ResearchBlogging.org
HULL, S., FAYEK, M., MATHIEN, F., SHELLEY, P., & DURAND, K. (2007). A new approach to determining the geological provenance of turquoise artifacts using hydrogen and copper stable isotopes Journal of Archaeological Science DOI: 10.1016/j.jas.2007.10.001

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Chaco Amphitheater

There’s a spot near the west end of the Pueblo Bonito parking lot, close to the spot where guided tours begin, where you can yell something in the direction of the canyon wall and hear a very clear echo back.  Some of the tour guides at Chaco regularly demonstrate this impressive effect when beginning their tours, and it’s certainly an interesting way to capture people’s attention.  I never did it myself; I’m generally averse to this sort of thing because I’m never confident that I’ll get it quite right, and it would be very awkward if I tried it and it didn’t work.  (There’s a similar effect in Statuary Hall in the US Capitol which I never demonstrated when I gave tours there either.)  This is kind of silly, though, and says more about me than about the echo.  In general I think highlighting this kind of acoustic effect is a good way to show just how special Chaco is, and while this particular echo is in a very accessible location there are many other places in the canyon with similar characteristics.  There are several places in and around Pueblo Bonito where you can hear with crystal-clear precision everything people say up on the Threatening Rock overlook, and there are some spots where you can even hear things clear across the canyon.

Secret Passage into Casa Rinconada

These effects have been known to the park’s interpretive staff for a long time, but until recently they’ve received very little attention from scholars.  In the past few years, however, the growing field of archaeoacoustics has begun to look rigorously at echoes and other acoustic phenomena in the canyon with an eye to understanding what role they may have played in Chaco’s past.  Rich Loose, a former archaeologist and old Chaco hand, has been at the forefront of this research, in collaboration with our old friends John Stein and Taft Blackhorse.  Rich recently sent me a couple of articles of his that have recently been published on this issue, along with a paper by John and Taft that I don’t think has been published anywhere.  The most important of these articles, I think, is one in which Rich describes in detail the research the team has done at the so-called “Chaco amphitheater” between Pueblo Bonito and Chetro Ketl.  Using sophisticated recording equipment and acoustic analysis software, they made a series of recordings of different sounds produced in various locations in and around the amphitheater and determined many of its important acoustic properties.  They also examined the cliff face in this area and concluded that there was considerable evidence that it had been deliberately sculpted, perhaps to improve its acoustic properties or for other purposes related to its use as a performance venue.  There is some evidence that there may have been a masonry wall along at least part of the sculpted area which could have created a “backstage” for performers, which Rich compares to the “secret passage” at Casa Rinconada.  There are also three large holes in the cliff face which appear to be natural but may have been enhanced as well.  One of these is large enough to fit a person and leads to a small cave that can apparently fit multiple people (though presumably in very close quarters).  Again, this has interesting implications for possible stagecraft.

Pueblo Alto and New Alto from Tsin Kletzin

One of the most interesting discoveries in Rich’s paper involves a small hill on the other side of the canyon, near Casa Rinconada, which he concludes was almost certainly deliberately constructed artificially for some purpose related to the amphitheater.  This hill, which is quite prominent and which I have often wondered about, apparently doesn’t show any sign of covering up a small-house site like the ones surrounding it, but neither does it appear to be natural.  It is, however, located almost exactly on the line along which sound from the amphitheater focuses, which also seems to coincide almost exactly with the north-south line between Tsin Kletzin and Pueblo Alto.  Sounds played from the hill could be clearly heard in the amphitheater, although their source could not easily be ascertained from there, and even speech from the hill could be heard in a somewhat garbled manner.

Canyon Wall from Pueblo del Arroyo

As with archaeoastronomy, archaeoacoustics suffers from the persistent problem that there’s no way to know for sure if the patterns it discovers are real or due simply to coincidence.  Rich is quite open in acknowledging this shortcoming in his articles.  In the absence of any means to verify results completely, a compelling combination of separate types of evidence is the best way to support an argument that the acoustic properties of a place are not accidental but reflect conscious decisions on the part of ancient people.  In the case of the Chaco amphitheater, I think Rich’s results clearly meet this standard.  Again as with archaeoastronomy, it’s hard to say what the specific implications of all this are for understanding prehistoric behavior, but in this case the acoustic evidence seems to shed at least some tentative light on several mysteries about Chaco.

Huerfano Mesa from New Alto

One of these is the nagging question of why Chaco was chosen in the first place as the location for such a grandiose center, given that it has no apparent natural resources and is in a particularly harsh and inhospitable location even by local standards.  The acoustic properties of the canyon walls, however, which as I noted above are not limited to the phenomena at the amphitheater specifically, provide one possible answer.  The main way in which Chaco does differ from the surrounding San Juan Basin is that it is, of course, a canyon, and has a long stretch of exposed sandstone cliffs with acoustic effects that can’t be found in many other places nearby.  This doesn’t necessarily explain its advantages in a larger geographic context, of course, and there are many other places just a bit further away with similar sorts of cliffs, but it does potentially shed some light on the question of what leverage the Chacoans would have had over other people in the area that they could use to gain their important position in the region.  People often gesture vaguely to “spiritual authority” or something similar in trying to explain this, but the acoustics provide an explanation for how a reputation for spiritual power could arise in the first place.  The position of the amphitheater at the center of the canyon, at the intersection of many alignments between buildings, certainly suggests that it was an important focal point for the area, and the acoustic characteristics are very suggestive.

Looking East from the Pueblo Alto Trail

Since this research involves John Stein and Taft Blackhorse, of course, Navajo oral traditions also enter into the story.  Specifically, the unpublished paper by John and Taft talks about a connection between the amphitheater and a ritual involving the use of the hallucinogenic datura plant, as well as a connection to the Great Gambler (specifically that the Gambler came to Chaco to take advantage of the powers associated with the amphitheater).  Indeed, they even say that the amphitheater is still used by “Navajo ceremonial practitioners,” which Rich incorporates into his articles as a key piece of evidence backing up his acoustic studies.  I’m a little dubious about a lot of this, and I intend to look into it further, but I do think oral traditions are an important place to look for an independent line of evidence to serve as a check on conclusions derived from archaeoacoustic (and archaeoastronomical) research.

Shell and Jet Display at Chaco Museum

Another issue this acoustic research sheds light on is the remarkable number of musical instruments, many quite elaborate, found in excavations at Chaco.  Almost all of these were found at Pueblo Bonito; the flutes in Room 33 are probably the best known, but I want to focus here on the conch shells apparently used as trumpets, which were also quite numerous and found in many rooms at Bonito.  Rich mentions these in his articles as well, although he doesn’t go into great detail about them.  He does, however, note that a conch shell trumpet was one of the sound sources he used in his archaeoacoustic research, and adds this interesting statement:

I found the shell trumpets to be one of the easiest ways to produce a loud stimulus for an echo. They are simple, easily portable, don’t require batteries, and are nearly foolproof once you master the technique of blowing one.

As luck would have it, Barbara Mills and T. J. Ferguson have recently published an important article on shell trumpets in the prehistoric Southwest in which they record all the places they have been found and try to see what conclusions about prehistoric ritual and ideology can be drawn from the distribution of trumpets through time and space.  They conclude that there are at least two separate ideological systems associated with shell trumpets: one having to do with the plumed serpent and associated with rain and agricultural fertility, and another having to do with warfare and healing (these might be two separate traditions, in which case there would be a total of three traditions).  Temporally, they find that the plumed serpent tradition, which is quite strong at Hopi and Zuni today, appears rather suddenly in the early fourteenth century, a time of considerable population movement and cultural change, and may have something to do with influence from the major center at Casas Grandes in Chihuahua as well as with migration of large numbers of people from the southern Southwest into the Pueblo region.  During this period conch shells are found primarily at Casas Grandes and in a large area of east-central Arizona along the Mogollon Rim, as well as in the Hohokam region of southern Arizona and as far east as Pecos.

Kiva A at Pueblo Bonito from Above

There is basically no evidence for plumed serpent iconography earlier than AD 1300, although there are conch shells.  Their distribution is much more limited, however, being confined essentially to the Hohokam region and Chaco, although there is one isolated example from the Mimbres area of southwestern New Mexico.  The geographic isolation of Chaco is striking on their map of sites where conchs have been found; there don’t seem to be any examples from any other sites on the Colorado Plateau during this period, despite the large population of this area and the presence of many strongly Chacoan-oriented or -influenced regional centers.  Apparently there were no shell trumpets even at Aztec, which is in general pretty similar to Chaco in the numbers and types of valuable artifacts found.  There were a bunch of them at Chaco, however, at least 17 overall, and all except two of them came from Pueblo Bonito specifically.  Within Bonito they were generally found in significant locations such as rooms containing other rare artifacts and a wall niche in Kiva R, rather than in trash deposits, which suggests that they were particularly important items.  One was found in Room 33, and four were found in Room 38, which also contained many rare items of apparent ritual significance as well as macaws.  Others were found in Kiva A (the great kiva in the east plaza) and Room 6 (one of the earliest rooms in Old Bonito).  Clearly, then, conch trumpets seem to have been associated very closely not just with the Chacoan system or Chaco Canyon in general but with Pueblo Bonito specifically.  And Pueblo Bonito, of course, is right next to the amphitheater.  The combination of the impressive acoustics of the amphitheater with the exotic sound of the conch shell would likely have been pretty powerful, perhaps in more ways than one.

Intact Roof Beams in Room 6, Pueblo Bonito

So what light does this combination shed on the Chacoan system overall?  Well,  it’s hard to say for sure.  Mills and Ferguson make a strong case that the Chaco and early Hohokam conchs are associated with the warfare/healing complex rather than the plumed serpent one.  Evidence for this complex comes mainly from Zuni, where there are many stories about the use of a “Big Shell” that was used to magically defeat the enemies of the Zunis.  There is also an association between this shell and witchcraft, both in fighting it and in possibly causing it.

Shell Display at Visitor Center Museum

The (non-witchcraft-related) healing part of the complex comes from one of the medicine societies, best known at Zuni but apparently also present at Hopi and Zia, and historically at Laguna.  This society is apparently named for a “spiral shell,” and its rituals include shells, but otherwise it’s not clear how much it has to do with conch shells or trumpets specifically as opposed to shells more generally.  The songs of the society at Zuni are said to be in the O’odham language of southern Arizona, and its origin story mentions a series of long migrations.  To me this combination suggests a Hohokam origin about as clearly as is conceivable, and it’s possible that at least some of the Hohokam conchs, particularly the small ones that may have been used as standards on staffs rather than as trumpets, may have been associated with a precursor of this society.  As I said, though, I’m not totally convinced that conchs specifically have anything to do with this society.  Shells of all kinds were a very big deal among the Hohokam.

Chaco Amphitheater in the Snow

So, given all that, it seems likely that if any conch-related ritual complex in the modern Pueblos is related to the conchs at Pueblo Bonito it’s the Zuni Big Shell, associated with warfare and witchcraft.  This is certainly intriguing, especially given the odd and ambiguous evidence about Chaco’s connections to warfare, although I think it’s ultimately inconclusive.  As Mills and Ferguson point out, it’s entirely possible that some of these prehistoric complexes have no modern equivalents at all.  Indeed, given the massive series of cultural changes and migrations separating Chaco from the modern Pueblos, it would hardly be surprising that the ritual traditions closely associated with Chaco specifically would have been lost or abandoned in favor of newer (or perhaps older) rituals considered more suited to the changing times.  It’s noteworthy that there don’t seem to be any modern (Pueblo) practices involving a combination of conch trumpets and cliff faces with special acoustic properties, given the strong circumstantial evidence that the two were connected at Chaco.  Whether or not any modern practices involving shell trumpets can be traced back to Chaco, however, the evidence for their importance at Chaco itself at its height is evocative and provides a hint of what Chaco may have been like for the Chacoans, even if what we hear today is only a faint echo of what they heard then.
ResearchBlogging.org
Mills, B., & Ferguson, T. (2008). Animate Objects: Shell Trumpets and Ritual Networks in the Greater Southwest Journal of Archaeological Method and Theory, 15 (4), 338-361 DOI: 10.1007/s10816-008-9057-5

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