Archive for the ‘Weather’ Category

Lost City Museum, Overton, Nevada

Yesterday the water level in Lake Mead hit its lowest point since the lake was originally filled in the 1930s.  John Fleck was there to mark the occasion, and he has some interesting thoughts on this historic event.  The importance of this milestone is more symbolic than practical; the lake level has not yet become low enough to trigger an actual shortage of water.  Nevertheless, this is an important reminder of the importance of water in the Southwest and the brave new world it is entering as the climate changes and conditions become both drier and less predictable.


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Cliff Palace, Mesa Verde

Well, I said I would probably continue to do posts here while I was guest-blogging for Keith Kloor, and obviously that didn’t happen.  I did write some posts over there that would probably be of interest to my readers here, especially on the concept of “collapse” as applied to Chaco and Mesa Verde.  I’ll have some more posts here soon, but that’s what I’ve got for now.

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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.
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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Snow Ranger at Chaco Visitor Center

It’s snowing like crazy here in New Jersey right now.  Rutgers canceled all classes today and morning classes tomorrow, so I’ve got a lot of unexpected time off.  Seeing all this snow is reminding me, as always, of Navajo linguistics.  Words for “snow” play a disproportionately important role in understanding the history and dialectology of the Navajo language.

Snow-Covered Vehicles Parked at Chaco Visitor Center

As Edward Sapir noted in the paper on Navajo linguistic origins I discussed a little while ago, there are two basic “snow” terms in the Athapaskan languages.  One refers to snow lying on the ground, and the other refers to falling snow.  The terms don’t resemble each other at all, and there is no etymological relationship between them.  In Navajo, the “falling snow” term is chííl (usually used in the verb form níchííl “it is snowing” or “the snowstorm has arrived”), and the “snow on ground” term is yas in the western dialect and zas in the eastern.  As Sapir also notes, this is one of the very few native isoglosses differentiating the two dialects, which are completely mutually intelligible and differ mainly in that the eastern dialect has borrowed more vocabulary from Spanish.

Snow Ranger at Chaco Visitor Center Entrance

This dialect difference is odd, and hard to explain.  According to Sapir, and supported by the cognates he gives in other languages, yas is the older form, and forms with z are found in only a few Athapaskan languages.  Most relevant to the Navajo case is that some of the Apache languages, specifically Jicarilla, Mescalero, and Chiricahua, also have zas.  These are all Eastern Apache languages; Sapir doesn’t give a cognate from Western Apache, which is closer to Navajo (so close, in fact, that the two are largely mutually intelligible), but given the rest of the data the term, if it hasn’t been lost, would be yas.  To me this suggests that zas is probably a loanword into the eastern dialect from one of the Apache languages.  It seems odd that such a basic item of vocabulary would be borrowed, but since the languages are all closely related it becomes more plausible than it might be otherwise.  Also, since the eastern dialect is known for its greater number of Spanish loanwords, it makes sense that if either dialect were to borrow an Apache word it would be this one.

Snow-Covered Law Enforcement Vehicle at Chaco Visitor Center

So if the word zas was borrowed by the eastern Navajos from one of the Apache groups, when and where did this happen?  The number of possibilities is actually considerably more limited than might be thought from the linguistic similarities, since the Navajos in historic times were more often at war than at peace with the various Apache groups.  Relations were complicated, however, and trade and intermarriage are known to have occurred.  I think the most likely context for this borrowing, however, is a very specific historical event where the Navajos and some of the Eastern Apaches were thrown together against their will.

Snow-Covered Hogans, Shonto, Arizona

I am referring, of course, to the US government’s ill-conceived attempt in the 1860s to confine the Navajos and the Mescaleros to a reservation in southeastern New Mexico on the Pecos River, near Fort Sumner, at a place called Bosque Redondo.  The Long Walk in which the US Cavalry under Kit Carson rounded up the Navajos and marched them to this reservation is one of the key traumatic experiences suffered by the Navajo people, and it looms large in Navajo history.  Perhaps even worse, however, were the atrocious conditions at the reservation itself, due largely to the government’s terrible miscalculation of the number of people  it would have to hold.  The authorities didn’t have good information about how many Navajos there were, and it turned out there were way too many for the allotted land to support in any kind of humane condition.  The supplies the government provided were also grossly inadequate, and the suffering of the Navajos was acute.  Malnutrition and disease were rampant, and many people died in the four years before the government realized the project was a disaster and ended it in 1868.  By that time the Mescaleros, who were both less numerous and more familiar with the area, which was close to their traditional homeland, had just left and returned home.  The Navajos were too far from their own home to just do that, but they did manage to negotiate a new treaty that gave them a new reservation in the area where they had been living before the Long Walk.  They returned home and have been there ever since.

Sign at Shonto Trading Post, Shonto, Arizona

The four years at Bosque Redondo were traumatic, but they also involved contact with new people, products, and ideas for the Navajos.  Much of what is now known as “traditional” Navajo culture developed during this period, when the Navajos were introduced to manufactured tools, processed foods, and other products initially provided by the government and later, after the return, supplied by traders at trading posts throughout the Navajo country.  There was also ideological influence from the Apaches, and a couple of ceremonies taken from the Chiricahuas, and still named as such, have since become some of the most popular healing rituals among the Navajos, probably due in part to their being shorter and less expensive than traditional Navajo ceremonies.  I suspect that the word for “snow” may have been borrowed at this time under similar circumstances from the Mescaleros and/or the closely associated Chiricahuas.

People Sledding by the Side of the Road into Shonto Canyon, Shonto, Arizona

But if the Navajos borrowed the word zas from the Apaches at Bosque Redondo, why is it only present in the eastern dialect?  Shouldn’t both dialects have it?  Well, not necessarily.  Although the number of Navajos at Bosque Redondo totally overwhelmed the governments expectations, there were actually quite a few groups who were able to hide out in the rugged canyon country of Utah and Arizona and escape capture by the cavalry.  These groups were later joined by returnees, but they managed to preserve a slightly different variety of Navajo culture, less influence by the Hispanics and Apaches in New Mexico, which eventually managed to become today’s western Navajo cultural system.  The differences between east and west, with the boundary roughly corresponding to the Arizona-New Mexico border and the Chuska-Lukachukai-Carrizo mountain ranges, are subtle but many, and they have had important effects on Navajo politics and culture in the subsequent Reservation period, extending to this day.

Fajada Butte Obscured by Falling Snow

You can learn a lot from words if you look close enough.  Sapir’s article used the “snow” words for a very different purpose, to show that the ancestors of the Navajos were unfamiliar with agriculture but very familiar with snow, and both the semantic shift he describes and the fact that there are separate words for snow indicating if it is falling or on the ground strongly point to an origin for the language in the north.  The later dialect division I have discussed here, however, sheds some possible light on later developments after the arrival of the Athapaskans in the Southwest, whenever that took place.  Every little piece of evidence helps to fill in the puzzle of the past.
Sapir, E. (1936). Internal Linguistic Evidence Suggestive of the Northern Origin of the Navaho American Anthropologist, 38 (2), 224-235 DOI: 10.1525/aa.1936.38.2.02a00040

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Fajada Butte and Yucca from Visitor Center Courtyard

In between a bunch of depressing news about budget cuts, the latest edition of Southwestern Archaeology Today links to a couple of interesting articles with considerable relevance to ChacoOne is about turkeys; I’ll do a post on it later.  The other is a column by Marc Simmons in the Santa Fe New Mexican on Pueblo clothing and how it has changed over time.

Diorama at Chaco Museum

Interestingly, in my experience visitors to Chaco don’t actually ask about clothing very often.  This may be due to the influence of a diorama in the visitor center museum which seems to answer any questions they might have, since it shows people in the course of various daily activities attired in loincloths and little else, which is pretty common for “Indians” in museum dioramas.  This “all loincloths all the time” interpretation is also common in artists’ renditions of “what life was like” on interpretive signs at many parks.  There aren’t many of these signs at Chaco, but they are quite common at some other parks such as Mesa Verde.  This all has a powerful effect on people’s perceptions, I think, because visual impressions are both stronger and more vivid than anything that can be explained in words.  Indeed, a woman once asked me, referring to the diorama, why the Chacoans had worn anything at all.  To this day I’m not sure what preconceptions she was bringing to the diorama, but clearly its implication that “the Indians” didn’t wear much had led her down that cognitive path.  This strong effect of the visual image is unfortunate, however, because quite a bit is known about how the Chacoans probably dressed, and all the evidence available strongly indicates that the diorama is totally wrong.

"Pithouse Life" Sign at Mesa Verde

But back to Simmons.  He’s one of the most renowned historians of New Mexico, and I’ve mentioned him before for his excellent book on the history of Albuquerque.  His specialty is the Spanish colonial era, so his column on Pueblo clothing draws most of its information from Spanish documents.  Those documents begin with the earliest exploratory expeditions in the sixteenth century, and they are generally thought to be pretty reliable in their descriptions of the people the explorers encountered.   The main thing that impressed those explorers about the Pueblos was how “civilized” they seemed in comparison to the hunter-gatherer groups they had seen further south.  Indeed, the name “Pueblo” itself, deriving originally from these reports, refers to the people’s settlement pattern based on large, permanent towns.

Pueblo Display at Chaco Visitor Center

Similarly, the main comments the chroniclers had about Pueblo clothing were about how substantial it was.  Men typically wore kilts, and women wore a type of dress known as a manta, made out of large square pieces of cloth.  The main material used was cotton, which was grown in the low-lying river valleys, especially in the Rio Abajo region at the southern end of the Pueblo domain, and traded to the villages in areas where cotton can’t be grown.  This cotton was woven into cloth, always by men, and often in ceremonial contexts in kivas or other important spaces.  The Spanish also remarked on the use of tanned buckskin or gamuza as an alternative material for clothes, especially nice during the cold winters.  Another item useful for keeping warm was the rabbit-fur coat, made of strips of rabbit hide woven together by women.  Footwear consisted primarily of leather moccasins known as teguas.

"Ceremonial Chamber" Sign at Mesa Verde Showing Men Weaving in Kiva

This information comes from a few hundred years after the fall of Chaco, of course.  A lot had changed in Pueblo culture during that period, so it would definitely be a mistake to simply project the Spanish reports back in time.  Luckily, we don’t have to.  Due to the good preservation at Chacoan sites, and the even better preservation at the cliff dwellings occupied slightly later, many examples of clothing have survived, though generally only in fragmentary condition.  These materials largely substantiate the Spanish accounts: Cloth is typically made out of cotton (probably underrepresented in the archaeological record because it doesn’t preserve very well), and cloaks made of woven rabbit fur and turkey feathers are common.

Sandals at Chaco Museum

The moccasins and leather garments are not generally found, however.  There is no shortage of footwear, but it takes the form of sandals made of yucca fibers.  These are very common and there are some indications that they may have had ritual importance in addition to their everyday use.  Leather moccasins during this period are rare to nonexistent in the Chacoan area, but common among the Fremont to the north in Utah, and they are even considered a diagnostic feature of the Fremont culture.

Bison Statue in Downtown Colorado Springs, Colorado

At some point between the fall of Chaco and the Spanish entradas, then, leather clothing and footwear seem to have been adopted by the Pueblos.  One theory to explain this, along with various other changes in Pueblo society during this period, links it to increased contact with Plains groups starting in the fourteenth century.  Another theory sees the adoption of leather clothing as associated with a prolonged period of climatic cooling, perhaps associated with the beginning of the Little Ice Age.  These two theories are not mutually exclusive, of course, and I think they actually complement each other nicely.  One proposed way of tying them together is a model in which cooling weather on the southern Plains leads to bison beginning to venture further south than they had before, which leads bison-hunting Plains people to follow them and come into contact with the Pueblos, whose increasingly efficient irrigation agriculture gives them surpluses of crops that they can exchange for meat, hides, and other bison products.  It’s notable that trade networks during this period seem to be oriented along an east-west axis connecting the Pueblos to the Plains, whereas trade during earlier periods seems to have been more north-south and connected to Mesoamerica.

Looking East toward the Great Plains from Las Vegas, New Mexico

Of course, this theory is by no means universally accepted, and there are other ways to interpret the changes in Pueblo material culture during this time.  Still, coming back to clothing specifically, I think all of this shows that the “Diorama Indian” loincloth-based attire has more to do with the preconceptions of the people who made the dioramas than with what people at Chaco and elsewhere actually wore.

Close-Up of Diorama at Chaco Museum

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Exterior of Reconstructed Great Kiva, Aztec Ruins National Monument

One of the most interesting and potentially productive lines of research in Southwestern archaeology these days involves the use of chemical analyses of various archaeological materials to extract more information about the societies that used them than is apparent just from looking at them.  The oldest and most established type of research like this is radiocarbon dating, which has historically been used less in the Southwest than elsewhere because it’s both expensive and less precise than tree-ring dating, which was invented in the Southwest and has been extremely important in the study of its prehistory.  Lately, however, archaeologists in the Southwest have been using radiocarbon more and more, since it can be used on anything organic (useful for sites which produce no datable wood but plenty of other organic material) and it’s been around for so long that the dates are considered very reliable.  They’ve also begun to use some other techniques that are newer but have enormous potential, which is already starting to be realized, to illuminate aspects of the past that have been the cause of much debate.

Intact Roof at Aztec Ruins National Monument

The most important of these is strontium isotope analysis, which we’ve seen before in the analysis of the wood brought to Chaco for architectural use.  Like radiocarbon dating, strontium analysis is based on looking at the ratio of two isotopes of an element, one of which is stable and the other of which is produced by the radioactive decay of another element and therefore varies.  Unlike radiocarbon, however, strontium cannot be used for dating on archaeological timeframes, since the half-life of the radioactive decay process involved (the conversion of rubidium-87 to strontium-87) is 48.8 billion years.  It can, however, be used to identify locations, since the amounts of strontium and rubidium in different areas vary a lot and strontium is absorbed unchanged by organisms from their environment.  Thus, in theory, one could test an organic artifact for its strontium ratio, then compare that to the strontium ratios of the water or soil in various places where the artifact may have originated and figure out where it came from.  This would then allow all sorts of archaeological conclusions.

Intact Roof at Pueblo Bonito

Of course, it’s never quite that simple, as the case of the wood shows.  It was relatively easy to use this analysis for the high-elevation types of wood that occur in relatively few places in the Southwest, but when the technique was extended to the very common ponderosa pine beams the number of possible origins increased so much that few definite conclusions could be reached.  There is also the problem of making sure that the strontium ratios found in the archaeological material actually resulted from growth processes rather than contamination by later mineral deposits.  Since this technique is relatively new, the methodology for it is not yet totally worked out, and not every attempt to use it ends up working.

Row of Metates, Aztec Ruins National Monument

Both the promise and the pitfalls of strontium analysis are shown clearly by a new paper by Larry Benson of the United States Geological Survey.  Benson has made something of a name for himself as the main player in the increasingly important analysis of corncobs found in Southwestern archaeological sites.  Corn is a useful plant to use for this sort of thing for a number of reasons:

  • It’s pretty common, especially in sites like cliff dwellings and Chacoan great houses with especially good preservation of organic material.  The Anasazi depended heavily on corn for their diet, so there are corncobs all over the place.
  • It grows quickly.  This is not important from the perspective of strontium analysis, but it means that radiocarbon dating can provide a very accurate range of dates within which the corn was grown and eaten.  This is in contrast to slow-growing plants, such as trees, which have the problem that the part tested may happen to be much older than the date of use.  The combination of accurate dating with strontium-based source determination makes corn a very powerful source of information.
  • It bears directly on a variety of important cultural questions.  Since corn was the main source of food for the Anasazi, finding out if they were growing it themselves or importing it from elsewhere has major implications for models of cultural systems and their means of support.  This is a longstanding issue in the study of Chaco specifically.

This particular paper addresses several issues, both substantive and methodological.  Substantively, Benson analyzes a set of corncobs excavated from the Gallo dwelling in the Chaco campground in the 1950s and adds the data derived from them to the data from earlier studies of cobs from this site as well as from Pueblo Bonito and Chetro Ketl.  He also reports on strontium isotope ratios from several agriculturally productive areas of the Zuni Reservation and adds them to the previously reported data from other parts of the Colorado Plateau.  He then combines this new information with the previously reported data to draw some specific conclusions about the sources of some of the cobs.  Importantly, however, he does not come to any conclusions about the sources of the newly analyzed Gallo cobs.

Metate at Pueblo Bonito

The reason for this lies in the methodological side of the paper, which may be the most important in the context of overall research on this topic.  The cobs Benson reports for the first time here, unlike the previously analyzed cobs, were not burned, and part of the purpose of this research was to see if the procedures used to prepare and analyze the burned cobs could be used for unburned cobs as well.  As it turns out, they can’t, and the strontium ratios from the unburned cobs appear to come from post-depositional mineral contamination rather than growth conditions.  This seems to be because the act of burning effectively “seals in” the trace minerals in the cobs, protecting them from contamination.  While this result is somewhat disappointing, in that it means that the strontium data from the new cobs can’t be used to draw any conclusions, it is important in informing others that if they want to do this kind of research on unburned corn cobs they need to come up with new procedures.  In the course of doing this analysis Benson also uses some data on recent experimental growing of Pueblo varieties of corn in Farmington that provides valuable reference material on just how closely strontium ratios in corncobs can be expected to correspond to the ratios in the soil and water in the area.  The answer is closely, but not perfectly, which is also useful information for future researchers.

Keyhole-Shaped Kiva, Aztec Ruins National Monument

Despite those issues, however, this paper does include some important substantive conclusions.  Although the new cobs couldn’t be used for strontium analysis, they did produce radiocarbon dates, which correspond very closely to the dates on the earlier Gallo cobs as well as some of the ones from Pueblo Bonito and Chetro Ketl.  Interestingly, these dates all cluster tightly around the AD 1180s.  As Benson points out, this is after the major drought of the mid-twelfth-century, which is generally interpreted as marking the “collapse” of the Chaco system and the possible depopulation of Chaco Canyon.  It has long been known that the canyon was occupied later, from the late twelfth century until the total abandonment of the region during the “Great Drought” of AD 1276 to 1299, but it’s unclear if the population at that time consisted of a remnant from the earlier Chacoan occupation or a reoccupation by people from elsewhere who may or may not have been descended from the earlier Chacoans.  In any case, whoever the people were who lived in the canyon in the 1180s, these are their corn cobs.

Keyhole-Shaped Kiva at Pueblo Bonito

They didn’t grow them, though.  In what is probably the most interesting conclusion of Benson’s paper, and certainly the most surprising, he goes through a careful analysis of the strontium data, excluding the data from the unburned cobs, and finds that the values from the cobs do not overlap with any of the locations in the Chaco area, either in the canyon or around it, that have been tested.  It’s certainly possible that they come from somewhere nearby that hasn’t been tested, but at this point a lot of potential growing locations in and around the canyon have been analyzed, so there aren’t a whole lot of additional options.  It’s not a very promising area for agriculture, after all, and pretty much all of the obvious places have now been tested for strontium ratios.

Hubbard Tri-Wall Structure at Aztec Ruins National Monument

So if these cobs didn’t come from Chaco, where were they grown?  Benson compares their strontium ratios to data from several areas in and around the San Juan Basin: in addition to the newly reported Zuni sites, these include Lobo Mesa, the Red Mesa Valley, the Rio Puerco of the West, the Defiance Plateau, Chinle Wash, the Four Corners area, Mesa Verde, the Totah, and the Dinetah.  This covers almost the whole area once occupied by Chacoan outliers, and several places beyond.  The cob ratios turn out to overlap considerably with one of the Zuni areas, the Mesa Verde/McElmo Dome area, the Totah, the Defiance Plateau, Lobo Mesa, and the Rio Puerco valley.  For some reason Benson doesn’t mention the Puerco in the text of the article, but in the figure showing the boxplots of the values for the various regions it clearly overlaps a bit with the cob values.

Tri-Wall Structure at Pueblo del Arroyo

Unfortunately, the strontium analysis itself doesn’t provide any way to choose which of these areas is the most likely source of the corn.  Any of them is consistent with the evidence.  Benson therefore turns to other lines of evidence to narrow down the choice.  He eliminates Lobo Mesa and the Defiance Plateau because of evidence that they were not occupied during this period; he doesn’t go into a whole lot of detail on what this evidence is, which is unfortunate.  As I mentioned above, he doesn’t discuss the Puerco at all, which is also unfortunate.  This leaves Zuni, the Totah, and Mesa Verde as the remaining options.  These are all areas that had Chacoan outliers during the height of the Chaco system and probably experienced immigration of people from Chaco after the system’s collapse, and they were all home to significant populations during this relatively wet period, so they are all plausible sources of corn imported to Chaco.  Benson concludes that the Totah is the most likely source based on the fact that it is the closest of the three areas and the one that seems to have had the strongest connections to Chaco, and while he acknowledges that this is little more than a guess, it sounds plausible enough to me.  Certainly Aztec, which is often interpreted as a successor to Chaco in some sense, was a major center in the late twelfth century, as was Salmon, and the material culture of the people living in Chaco at the time shows considerable influence from areas to the north (although it’s not entirely clear how to interpret this).

Aztec West Great House, Aztec Ruins National Monument

This paper is part of a growing corpus of data, much of it contributed by Benson, showing that the inhabitants of Chaco at various times did in fact import corn to the canyon.  This seems to largely settle one of the longstanding disputes in Chacoan archaeology, and it further points out the pointlessness of trying to estimate the population of the canyon by first estimating its agricultural potential.  What remains puzzling is how this system would have worked, and why.  Beyond the obvious question of who was supplying the corn, which is partially addressed in this paper, the question of what leverage the canyon inhabitants would have had to get those people to supply them remains open.  This paper, in fact, seems to raise more questions than it answers in this respect.  While during the height of the Chacoan system it is relatively easy to come up with theories for how the canyon inhabitants could have acquired supplies from the surrounding area, in the post-collapse period, when the canyon population was tiny and regional importance had clearly shifted elsewhere, explaining how the few people left at Chaco managed to get others to grow food for them becomes a daunting task.  It’s this sort of challenge, however, that I think makes Chaco so fascinating and ensures that it will continue to be a place worth studying for a long time to come.
Benson, L. (2010). Who provided maize to Chaco Canyon after the mid-12th-century drought? Journal of Archaeological Science, 37 (3), 621-629 DOI: 10.1016/j.jas.2009.10.027

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Highly Deteriorated Vertical Intramural Beams at Pueblo Bonito

Highly Deteriorated Vertical Intramural Beams at Pueblo Bonito

I’ve been talking about climate change more than about Chaco lately, which is a pretty big shift from the earlier days of this blog.  In part this just reflects the major changes in my life: while before I was living and working at Chaco, now I’m going to school and spending a lot of time learning and thinking about things like climate change.  I’ve also, frankly, been getting a little bored with Chaco and archaeology, so I’m taking a bit of a break from it.  I’ll definitely come back to it at some point, don’t worry, but for now it’s not among my highest priorities.

Spruce Tree House, Mesa Verde

Spruce Tree House, Mesa Verde

One of the major points I’m trying to make with this blog, however, is that climate change and other environmental challenges today are by no means disconnected from Chaco and the past.  This is true in various ways, some more abstract than others, but a major report just released by the Natural Resources Defense Council and the Rocky Mountain Climate Organization (via Keith Kloor) on threats to national parks from climate change points to one quite concrete connection.

Mesa Verde from Escalante Pueblo

Mesa Verde from Escalante Pueblo

Like many other parks, Chaco is threatened by the effects of global warming, effects that are starting to become apparent in changes to weather patterns and climatic trends.  It’s not listed as one of the parks most at risk, although Bandelier and Mesa Verde are, but the fact sheet for New Mexico does describe Chaco as being subject to the same pressures as other parks in the region.

Light Snowfall on Fajada Butte

Light Snowfall on Fajada Butte

The main effects of climate change on these parks are decreased snowpack, the closely related problem of reduced water supplies, increased erosion resulting from heavier and more frequent downpours, and loss of flora and fauna as a result of habitat changes.

Entrenched Arroyo

Entrenched Arroyo

These are indeed serious problems, and pretty unambiguously linked to global warming, but they are matters of degree, not kind.  Problems of this sort have always been major concerns in the southwest, where water supplies and the vagaries of precipitation are and always have been hugely important to human settlement patterns and decision-making.  The intensification of these processes due to climate change is of major concern, but it’s not very flashy and it’s unlikely to attract much attention in and of itself.  No major catastrophes to grab headlines and focus attention are likely to result from these changes, but they are serious threats nonetheless.  As so often in the southwest, natural disasters are long and slow, subtly and almost imperceptibly changing the landscape until the status quo become untenable and major, often painful, changes suddenly become necessary.

Tributary Drainage in Chaco Canyon

Tributary Drainage in Chaco Canyon

This gives ample opportunity for people to react and to minimize the damage, of course, but it also gives little incentive for them to do so until it’s too late, which is what makes it so pernicious.  Life in arid environments is always lived on the edge, and the margin for error is minimal, so adaptation to a certain environmental context is always very risky, a huge bet on a particular outcome with unknown odds.  There’s a lot more I could say here about gambling as a metaphor for economic and environmental decision-making, but I’ll just leave it at that for now.

Storm Clouds over Fajada Butte

Storm Clouds over Fajada Butte

On a lighter note, I was amused to see this in the New Mexico fact sheet:

In some parks, such as Bandelier and Chaco, snow does not linger that long, but with less snow in winter fewer visitors would get to see the parks at their scenic best.

Chaco’s definitely at its scenic best in the winter, but I can say from experience that very few visitors ever see it.  Winter at Chaco is a very quiet time of year.

Fajada Butte Obscured by Falling Snow

Fajada Butte Obscured by Falling Snow

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