The Complications of Corn

Metate Incorporated into Wall Capping, Pueblo Bonito

I’ve written a bit about the recent research, spearheaded by Larry Benson of the USGS, into the sources of the corn found at Chaco.  These studies continue to refine the techniques used to identify source areas, but so far they have shown that corn was almost certainly being imported to Chaco both during and after the florescence of the Chaco system between AD 1030 and 1130.  As they begin to test more potential field areas, of course, the number of matches for the strontium isotope ratios in the corn at Chaco has increased.  While early studies indicated that much of it likely came from the Chuska Valley, it now looks much more likely that it instead came from the area along the Chaco River between there and the canyon.  This is an area with numerous outlying great houses, and it was probably the main route for the many commodities from the Chuska area that were brought to the canyon, and it’s also generally a better area for agriculture than the canyon itself, so this all makes sense.  There has also been some evidence that at least some corn was also coming from the Totah area to the north, again a more productive agricultural area with many Chacoan outliers.

Based on the proveniences of the corncobs from Pueblo Bonito that were tested early on, one tentative suggestion emerging from this research was that the main sources of imported corn changed over time.  The cobs that came from the lower Chaco River were from Rooms 3 and 92 in the northern part of Old Bonito, one of the earliest parts of the building to be built, while the one cob of possible Totah origin came instead from Room 170, in the southeast corner, one of the newest parts of the site.  Since there does seem on other grounds to have been a shift in the emphasis of the Chaco system from south to west to north over time, it would make sense that the early rooms contained early cobs from the west while a later room contained a later cob from the north.

Talus Unit with Snow

A paper published in 2008 by a group of big names in Chacoan studies sought to look at this directly by radiocarbon dating the cobs.  This is an interesting paper which goes beyond that narrow topic to also look at the characteristics of the corn found at the various great houses and other sites.  One of the co-authors is Mollie Toll, a specialist in archaeobotany who has done a lot of research on Chacoan corn.  As part of that research, she had long noted that the corn at Pueblo Bonito generally had bigger ears with more rows of kernels than most other corn known from the prehistoric Southwest.    It was bigger than earlier and later corn, for one thing, but it was also bigger than most other corn from the same period.  Corn from the Chacoan occupation of Salmon Ruin was also unusually large, as was corn from the Talus Unit behind Chetro Ketl, but corn from Pueblo Alto and Pueblo del Arroyo, other contemporary great houses at Chaco, was smaller and more in line with that from earlier and later sites.

Toll came up with three possible explanations for the difference.  Pueblo Bonito corn could be a different variety or “landrace” from the others, which is plausible but not directly testable with current technology.  It could also have been grown outside of the canyon where conditions were better for agriculture, while the corn from other great houses was grown in the canyon where conditions were poorer.  Finally, and problematically, the corn at Bonito might not have been Chacoan at all!  Since modern corn is generally bigger than ancient corn, Toll (when she was first looking at this in the 1980s) couldn’t exclude the possibility that the corn found at Pueblo Bonito had actually been put there by Navajos in the nineteenth century.  Much of it was from George Pepper‘s excavations in the 1890s, so it couldn’t be newer than that, but there was no way for Toll to tell how much older it was.

Room 3a/92/97, Pueblo Bonito

We still can’t tell different ancient landraces apart (although the recent sequencing of the maize genome may make this more feasible in the future), but the strontium isotope testing is giving us a sense of where the corn was grown, and accelerator mass spectrometry now makes directly dating the corn relatively easy.  Seven cobs from Pueblo Bonito that had been used in the strontium studies were dated for this paper.  One was the cob from Room 170 that possibly came from the Totah, one was from Room 92, and the rest were from Room 3.

The results were illuminating, but also challenging.  All the cobs clearly dated to ancient times, so the possibility that the size of Pueblo Bonito’s corncobs represents recent deposition is effectively quashed.  Three of the Room 3 cobs had closely clustered dates with intercepts around AD 1000, which offered some partial support for the idea that the corn in the early rooms was relatively early, but the other two were widely spaced, one at 870 and at 1170.  This is problematic for the idea that the date of corn in a room can be predicted from the date of that room’s construction, but it makes sense that the deposits in a room may date to well after its construction.  Since Room 3 dates very early, probably to the 900s, it’s likely that the deposits there resulted from much later trash dumping once it was no longer used for its original purpose.  Room 3 has a firepit, so it was probably originally a residential room, and it is likely one of those “big square rooms” that I have argued began to take the place of kivas in Chacoan room suites of the tenth century.  Room 92 is part of the maze of confusing rooms next to Room 3.  It had a well-preserved floor with corn and bean bushes on it (it’s not clear from Pepper’s description if this was the second or third floor), which suggests that it was used as a storeroom at the end of the period of occupation in this part of the building.  The cob from this room had the latest date of any in the study, with an intercept of AD 1220, which is consistent with the idea that this room was in use as a storeroom at the end of occupation.

Room 170, Pueblo Bonito

The biggest surprise, however, was the cob from Room 170, which dated to AD 1010.  This is particularly odd, since Room 170 was probably built around 1080 or even later.  Looking at the probability curve for this date, there is some chance that the actual date was around 1100, but the curve as a whole has a much more prominent peak around the intercept at 1010 than any of the other reported dates, which suggests that the probability is quite high that the intercept does in fact represent the true date or close to it.  The authors give various possibilities for why the cob might have been placed in this room long after it was grown, including the idea that it was put there as some sort of ritual offering of continuity with the occupation of earlier parts of the building.  I prefer another explanation they also suggest, which is that it was part of an earlier trash deposit that was redeposited in Room 170 for some reason.  There is very little information on what the deposits in this room were actually like, but many of the rooms in this part of the building were full of trash when excavated, and I think it’s most likely that this one was too.  The trash could have been put there for any number of reasons; if it was redeposited from somewhere else, it may have served as structural fill to support an upper story.  In any case, this puts a damper on the idea that the overall sources of corn changed over time.  Indeed, the sources seem to have been pretty constant through time for cobs left in different areas of the site, which suggests that the real story is much more complicated.

One nice thing about this paper is that the authors do a very good job of properly reporting their radiocarbon dates, particularly in giving point estimates as intercepts, which are meaningful, rather than midpoints, which are not.  Many papers make this mistake, including some of Benson’s reporting these and other dates on corn.  This paper also shows the probability curves for the dates, which give even more information.  This seems to be pretty common these days among Mesoamerican archaeologists, but it’s still quite rare in the Southwest, where radiocarbon dating has only recently become a major focus.  The availability of tree-ring dates, which are much more precise, has generally led Southwestern archaeologists to neglect radiocarbon, but it’s becoming increasingly obvious from studies like this one that the ability to date things other than trees is very useful in interpreting sites.

Obviously this paper just reports a handful of dates, and the authors take pains to point out the tentative nature of any conclusions they draw, but it’s an important contribution to the issue of where the Chaco system, whatever its nature, was getting its means of support.  As is often the case with new avenues of research, at this point papers like this pose more questions than they answer, but there are plenty of corncobs out there to date and analyze in other ways, just as there are plenty of potsherds to test for theobromine.  Once we get a bigger database of dates and strontium (and other) ratios, we’ll start to get a clearer picture of the behavior behind these remains.

Metate Fragment at Pueblo Alto

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Chocolate Everywhere!

Display Case at Chaco Museum Showing Cylinder Jar and Canteens

I mentioned earlier that there was a new paper out on chocolate at Chaco that I needed to read.  I read it today, and it’s quite interesting.  One of the most interesting things about it is that it’s by a different group of researchers than the first one and uses somewhat different methods.  As far as I can tell, all the study of chocolate residue in archaeological pottery until this paper has been done by Jeffrey Hurst at Hershey, in collaboration with a variety of archaeologists.  Except for the Chaco paper he did with Patricia Crown, all of Hurst’s work in this area has been on Mesoamerican pottery and in collaboration with Mesoamerican archaeologists.  This makes sense, since Mesoamerica is where chocolate is grown and was used most extensively in antiquity.  Hurst’s methods involve scraping residue from the interior of pots or grinding up potsherds to test them for the presence of theobromine, a chemical compound that serves as a biomarker for chocolate.  They aren’t hugely destructive methods, as analytical methods applied to artifacts go, but there is a certain amount of damage inherent in the scraping (and more in the grinding, of course).

This new paper pioneers a different method, which uses a wash of deionized water on whole vessel interiors (this could presumably be done with sherds too, but these authors used whole vessels) and subsequent analysis of the water with a very sensitive mass spectrometer.  The researchers are not affiliated with Hershey, but instead with Bristol-Myers Squibb, except for the lead author, Dorothy Washburn.  Washburn has for many years now been studying symmetry patterns on pottery and other artifacts and she has come up with a variety of interpretations of social structure and change from the patterns she sees.  The work she has done on Chaco has led her to posit that the “special” vessel forms associated with the Chaco Phenomenon, particularly cylinder jars but also pitchers and shallow bowls, show a very different type of symmetry from that prevailing on Pueblo pottery before and after Chaco.  In publications such as her chapter in the Salmon Ruins synthesis volume, she further contends that this sudden difference indicates an influx of people from elsewhere with a very different social structure, and she points to Mexico as the most likely source given the presence of both similar symmetries and similar vessel forms there.  This puts her in what I’ve called the “hard Mexicanist” camp, not a popular position among Chacoan scholars these days (although this chocolate stuff may start to change that).  I don’t really buy her arguments for physical migration of Mesoamericans to Chaco, and I think she generally goes a bit too far in inferring specific social structures from the abstract symmetries she studies, but her evidence for a big difference between Chacoan and other designs is solid and well-taken.

Cylinder Jar at Chaco Museum from Above

Given Washburn’s theories, it makes sense that she would jump at the chance to look for chocolate residue in Chacoan vessels.  The Crown and Hurst paper that started all this really came out of nowhere; no one in the Southwest was expecting it at all, and it’s likely to end up being one of the major turning points in interpretations of Chaco.  The paper itself, though, was short, and the research behind it was modest in scale.  Crown and Hurst only tested five sherds from the mounds in front of Pueblo Bonito, three of which seemed from their curvature to be from cylinder jars while one of the others was from a pitcher and the final one could have been from either a cylinder jar or a pitcher.  Testing revealed that the three definite cylinder jar sherds showed evidence of chocolate, while the other two didn’t.  This was remarkable, groundbreaking stuff, to be sure, but it was still only five sherds.  The really important thing about that paper was that it opened up the possibility of running tests like this on all sorts of sherds and vessels to determine the extent of chocolate use in the prehistoric Southwest, and it seems Washburn was inspired to take it a step further.

Room 28 at Pueblo Bonito

She and her coauthors, William Washburn, who I presume is her husband, and Petia Shipkova, both of whom work for Bristol-Myers Squibb’s Pharmaceutical Research Institute in Princeton, NJ, apparently developed this new technique for doing the theobromine testing and they applied it not to sherds but to whole vessels.  Not just any whole vessels, either; they went straight for the important ones: the cylinder jars from Room 28 at Pueblo Bonito, along with cylinder jars, pitchers, and shallow bowls from burial rooms elsewhere in Bonito (including Room 33).  They also tested three cylinder jars from Pueblo del Arroyo, at least two of which are of plain redware rather than the whiteware that characterizes all other known cylinder jars (there is some confusion over whether the other jar is red or white, in that the paper says all three are red but the National Museum of Natural History catalog seems to say that one is white).  In addition, they tested a variety of similar forms from the Hohokam site of Los Muertos.  This is interesting, because the Hohokam in southern Arizona showed a wide variety of Mesoamerican influences to a much greater degree than Chaco ever did, and one of the first things I wondered when I read the Crown and Hurst paper was whether a similar study of Hohokam vessels would also show chocolate use.  They picked Los Muertos specifically because it’s a Classic-period platform-mound complex with what appear to be elite burials.  The platform mounds of the Hohokam Classic are the only other phenomenon except for Chaco in the prehistoric Southwest that show clear evidence of social hierarchy, and the authors of this paper clearly chose this set of vessels to see if chocolate use corresponded to increased hierarchy.  In all they tested 57 vessels from Chaco great houses and 10 from Los Muertos, and as a control they also tested eight vessels from small sites at Chaco, on the Little Colorado River in Arizona, and in southwestern Colorado.

Pitchers at Chaco Museum

What they found was that most of the great-house and Hohokam vessels did indeed test positive for theobromine.  Specifically, 80% of the Los Muertos vessels tested positive, as did 65% of the Chaco cylinder jars, 41% of the Chaco pitchers, and 83% of the shallow bowls from Chaco.  The lower percentage for the pitchers may indicate that they were used for a variety of things, not just chocolate, which might in turn explain why Crown and Hurst’s pitcher sherd tested negative.  The very high number of positives for the shallow bowls is very interesting, and suggests that this class of vessels, largely overlooked because they resemble local forms more than the cylinder jars, may be more important than people have thought.  On the other hand, only 12 bowls were tested (versus 23 cylinder jars and 22 pitchers), so this could just be a fluke of sampling size.  These results seem to confirm the Crown and Hurst results and reinforce the idea that the presence of chocolate, a clear sign of ongoing trade and contact with Mesoamerica as well as acceptance of Mesoamerican ideas and practices, may correlate strongly with the evidence for social hierarchy at both Chaco and the Classic Hohokam platform mounds.

But wait, what about the small-house sites?  Here’s where things get really interesting, in an unexpected way.  All eight vessels from the small houses tested positive for theobromine.  This was totally unexpected, and the authors devote quite a bit of discussion to this result.  Apparently concerned that there might be a problem with the whole theobromine-testing enterprise, they went looking for native plants in the Southwest that might contain theobromine.  If there were any, of course, that would call all of these results into question.  They couldn’t find any, so it does seem (unless there’s something amiss with their experimental protocols) that the results for the small houses really do indicate that chocolate was not just confined to the great houses at Chaco and the platform mounds in Phoenix.  They suggest that commoners might have been paid in chocolate for their work for the great-house elites, a very interesting idea.  In Mesoamerica cacao beans were often used as currency, and if something similar was going on at Chaco that would be cause for some serious rethinking of how the Chacoan economy worked.

Bc 51

One issue that the authors don’t really address is that the small houses they picked are all within areas that could plausibly have been part of the Chaco system, so there isn’t really an independent check here on how widespread chocolate was in the region as a whole.  They preferentially selected vessels from early excavations because early excavators usually didn’t wash the vessels they found, which makes sense for this type of project but also means that provenience information for the small sites is not ideal.  Nevertheless, one of the small houses that produced these vessels was Bc 51 at Chaco, which is right across the canyon from Pueblo Bonito and would obviously have been closely incorporated into the Chaco system.  The others included a cluster of sites in the Montezuma Valley of southwestern Colorado, which is an area with several nearby Chacoan outliers, and a site on the Little Colorado River in eastern Arizona that is not located very precisely but could have been relatively close to the far western edge of the Chacoan system.  There are several major outliers along the Rio Puerco of the West, a major tributary of the Little Colorado, and some evidence for at least a small amount of Chacoan influence as far west as Winslow.

Further testing of vessels and sherds from a wide variety of sites and time periods should help to clarify this picture.  The great thing about this chocolate stuff is that it’s all about analyzing pottery, which is by far the most common type of artifact found at sites in the Southwest.  There are vast numbers of vessels in museums throughout the country that could easily be tested using these techniques, and even vaster numbers of sherds collected from sites throughout the region that could potentially produce an unbelievably huge and detailed database of information on the distribution of chocolate in the prehistoric Southwest.  There are a lot of questions still outstanding at this point, but there is also a huge opportunity to try to answer them.  Hopefully this question will keep a lot of archaeology grad students set for thesis and dissertation topics for years to come, and the rest of us will benefit from the information they find and the patterns they discover.

Washburn, D., Washburn, W., & Shipkova, P. (2011). The prehistoric drug trade: widespread consumption of cacao in Ancestral Pueblo and Hohokam communities in the American Southwest Journal of Archaeological Science, 38 (7), 1634-1640 DOI: 10.1016/j.jas.2011.02.029

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Back to the Square Rooms

Peñasco Blanco

Returning to my theory that the large square rooms with hearths and other residential features found at some great houses in Chaco and elsewhere were in some sense replacements for earlier kivas, I think the best evidence for this at Chaco itself (as opposed to at outlying great houses like Salmon) comes not from Pueblo Bonito, which is just too complicated a palimpsest to make something like this easy to see, but from the other early great houses: Una Vida and Peñasco Blanco.  These at least seem to have simpler layouts than Bonito, though the extent to which this is just an effect of their being (mostly) unexcavated is unclear.  Nevertheless, at least some parts of these two great houses do seem to show basically the pattern that I’m proposing for the development of residential room suites at great houses.

To recap the idea: The very earliest great houses, those built in the AD 800s, seem to show a pattern of suites similar to that seen at small houses or unit pueblos, with each suite consisting of one rectangular room backed by two smaller rooms.  In front of each roomblock there are subterranean kivas, usually with slightly fewer than would be expected if each suite had its own kiva.  This suggests to me that the suites housed individual nuclear families, but that they were grouped into larger units, perhaps extended families, which shared kivas.  Whatever rituals these residential units would have conducted would probably have been in the kivas, but for the most part these were still residential structures, similar to the pithouses occupied in earlier centuries but with some of their functions transferred to the rectangular front rooms of the roomblocks.  The smaller rooms in the back would have been used for storage.  A typical great house would contain a few of these suites, with a kiva for every two or three.  It’s unclear what the relationships among different kiva-units within a great house would have been, but they could have either been separate extended families within the same real or fictitious “clan” or “lineage,” or they could have been separate lineages that were politically or ceremonially allied.  Importantly, all of these buildings are still residential at this point, although the residents may well host rituals or feasts open to the whole community either to solidify their political authority or because generosity is expected of them in exchange for community acceptance of their greater wealth or political/religious authority.  The main difference between great houses and small houses is just that great houses are bigger, with multiple stories in some instances and generally bigger rooms, as well as more extensive use of masonry rather than adobe or jacal construction.

Room 330, Pueblo Bonito

Then, at some point in the 900s, a change takes place in some (all?) great houses.  Use of the kivas is discontinued, and instead the activities that had been conducted in them are transferred to square surface rooms added onto the existing roomblocks.  This definitely seems to be what happens at Una Vida and Peñasco Blanco, although the extent to which there were earlier kivas is unclear given the lack of excavation.  In great houses newly begun during this time (it’s unclear how many of these there were in Chaco itself, but Kin Nahasbas may be an example), room suites were built without any kivas but with large, square rooms in front and smaller rectangular rooms varying in number behind them for storage.  This pattern continues well into the 1000s, at least at some great houses, and it’s associated with the very formal, symmetrical, rectilinear layout seen at sites such as Hungo Pavi, Chetro Ketl, and Pueblo Alto.  Some outlying great houses, such as Kin Bineola and (especially) Salmon, show this pattern as well.  Salmon seems to show that new great houses with (almost?) exclusively square rather than round living rooms were still being built as late as 1090, and if the early construction at Aztec is in the same pattern, which seems to be a matter of some dispute, it would still be going on well into the early 1100s.  This is probably also what we see at Pueblo Bonito too, with the possible addition of square rooms like 329 and 330 to the older suites at the west end of Old Bonito and the later addition of linear suites to the south of these rooms at the southwest corner of the site.

At some point in the late 1000s, however, a different type of room suite begins to arise at some Chaco great houses.  This is still a linear suite, sort of, but it consists of a round kiva built aboveground into a first-story square room, with one or two rows of two- or three-story rectangular rooms extending back from it.  These are the “blocked-in” kivas that are probably the most famous innovation of Chacoan architecture.  I see them as still residential spaces, in combination with the rooms behind them.  Their appearance at most outlying great houses indicates residential use of those sites, perhaps by local elites.  It’s not clear what the relationship is between these plaza-facing blocked-in kiva suites and the “elevated” kivas surrounded by rectangular rooms that start to appear at the centers of the rectilinear great houses with the square living rooms around this same time.  If those rooms are still residential, they’re pretty damn fancy residences.  They’re also quite unlike the other residential rooms at these sites, which are still square.  The “Tower Kiva” at Salmon is one example, as are the corresponding kiva at Hungo Pavi and the numerous examples at Chetro Ketl.  The central placement and unusual elaboration of these structures has led many to assume that they were ceremonial rather than residential in function, but I’m not so sure.  These sites do generally have great kivas, which pretty much everyone agrees were community-scale ceremonial/integrative structures, and they look quite different from elevated kivas (although it’s not clear to what extent the unique features of great kivas are due to structural requirements following from their size).

Kivas in the Southeast Part of Pueblo Bonito

In any case, the best examples of the plaza-facing blocked-in kiva suites are at Pueblo Bonito in the southeast and southwest wings.  These appear to have been built over earlier construction, so it’s not totally clear what was going on with these multiple, quite rapid changes in site layout during this period.  Again, though, they’re also obvious at Una Vida and Peñasco Blanco, where some (but not all!) of the earlier square living rooms are replaced by blocked-in kivas.  This also appears to have happened in the west wing of Chetro Ketl, but it’s unexcavated so it’s hard to say for sure.  There definitely are two blocked-in kivas there, though, and they appear to have rooms behind them like at Pueblo Bonito.

Then, at some point toward the very end of the eleventh century or very early in the twelfth, a totally new type of room suite begins to appear at Chaco great houses.  This is the famous “McElmo unit,” with a central blocked-in kiva surrounded on three or four sides by rectangular rooms, most of them significantly higher (three or four stories), creating a sort of “patio” over the kiva.  These rarely have ground-floor exterior walls, and they are remarkably uniform and modular in form.  The most famous of these structures are the freestanding ones, including New Alto, Casa Chiquita, and Kin Kletso (which comprises two adjacent units), but clearly analogous forms can be seen within certain great houses, including the north and south wings of Pueblo del Arroyo and the Kiva B complex at Pueblo Bonito.  Similar units that are just outside of existing great houses can be seen at Chetro Ketl and Peñasco Blanco.  The masonry of most of these is very different from that used at earlier great houses, being composed of blocky yellow sandstone rather than fine, hard, dark sandstone, and this has been used to argue that they represent influence from the north.  The masonry may indeed reflect northern influence (though in a different way from what the original proposers of this idea thought), but the form predates the shift in masonry and probably developed locally in Chaco.

Kiva E, Kin Kletso

There has been a lot of debate over the function of McElmo units.  Some see them as warehouses, while others see them as ritual (or possibly astronomical) special-use sites.  I’m increasingly thinking that all this speculation is based on an overemphasis on their differences from earlier great houses, and that they were probably residential and represent the final version of the Chacoan room suite.  More on this later.

McElmo units may represent the final development of Chacoan architecture in terms of form, but the great houses continued to be occupied for quite some time after the construction of these roomblocks in the early 1100s.  What we see at this point is an increased emphasis on the blocked-in kiva concept, with new kivas, often of “non-Chacoan” form, being built into earlier square or rectangular rooms.  Some call these “intra-mural” rather than “blocked-in” kivas, to emphasize that they were built into earlier rooms rather than having square rooms built around them, and I think this is a helpful distinction.  These really proliferate at Pueblo Bonito late in the occupation period, and this also happens at Aztec and Salmon during their “post-Chacoan” (also called “secondary” or “Mesa Verdean”) occupations.  At the same time, many great houses also see the construction of new subterranean kivas in the plazas, often with accompanying small blocks of square rooms.  These aren’t usually datable directly, but they appear to be very late.   Pueblo Bonito has particularly many of these, and there are a few in the southeast corner of Chetro Ketl too.  These appear to represent the construction of typical small-house or unit-pueblo style residential units within earlier great houses, and they may or may not represent an occupational discontinuity of some sort.

So basically, what we see is a sequence of underground kiva to above-ground square room to above-ground kiva.  There are plenty of variations and complications, but that’s the general sequence.  The later use of intra-mural kivas, especially at Pueblo Bonito, has tended to obscure the middle stage here, but it really seems to represent something meaningful at least as a chronological marker in Chacoan architecture.  Does it mean anything else culturally?  That part I’m still looking into, but it may.

Fajada Butte from Una Vida

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Salmon Ruins and Chacoan Residence Patterns

Salmon Ruins Sign

One of the largest and most important of the “outliers” associated with the system centered on Chaco Canyon in the late eleventh century AD is Salmon Ruin on the San Juan River near Bloomfield, New Mexico.  Salmon is about 45 miles due north of Chaco, and its location in a fertile river valley makes it a much less surprising (though still impressive) site than Chaco, with its stark, desolate setting.  Salmon was partly excavated in the 1970s by Cynthia Irwin-Williams of Eastern New Mexico University, and the Center for Desert Archaeology has recently been working on an extended project to collect, reevaluate, and publish data from those excavations as well as new analyses taking into account more recent discoveries and interpretations relating to the Chaco system in general.  One result of this was the publication of a comprehensive three-volume site report in 2006, and another was the publication of a shorter, more synthetic volume in 2008.  I read the report a while ago and am currently about halfway through the newer book.  It’s definitely more accessible than the report, but it doesn’t really stand alone.  A lot of basic information about the site and the excavations seems to be assumed, presumably because it’s discussed in the site report.  The report doesn’t stand alone either, and in general there’s a surprising lack of overlap between the two publications.  You might think that the synthetic volume would be a more accessible book aimed at a general audience, since it’s published by a university press rather than by CDA and the Salmon Ruins Museum, but while the new book goes well beyond Salmon itself in discussing the archaeology of the “Middle San Juan” or “Totah” region in general it really seems to be aimed at specialists with substantial background who have either already read the site report or are willing and able to find and read it if they want to follow up on the numerous references to chapters in it.  Both books are very expensive, which is another factor standing in the way of a general audience for them.

This is all rather unfortunate, because there’s a lot of important and fascinating information in these two publications.  In the context of my recent discussion of kivas at Chaco and the debate over their function, one of the chapters in the synthetic volume is particularly relevant.  Here Paul Reed, the head of the CDA project at Salmon, makes a strong case for a largely residential function for Salmon during the Chacoan period.  This is interesting in itself due to the longstanding debate over the function of great houses like Salmon in general, with some arguing that they served as primarily non-residential ceremonial structures while others see them more as elite residences.  Reed doesn’t discount the importance of ritual functions at Salmon, nor does he try to argue that all great houses were primarily residential, but he shows from the evidence collected by the excavations in the 1970s that there is abundant evidence for residential use of many of the rooms at Salmon during its brief Chacoan occupation as well as during its longer subsequent occupation, which he sees as being by local people after the Chacoan residents left and went to Aztec.

Excavated Rooms at Salmon Ruin

One of the most important pieces of evidence Reed points to to support a residential function at Salmon is the very obvious presence of room suites throughout the site.  Salmon has a very formal, “planned” layout typical of later great houses, which makes sense since it seems to have been founded around 1090, toward the end of the Chacoan era (which lasted from about 1030 to 1130).  Indeed, it looks virtually identical in layout to Hungo Pavi, an unexcavated great house in Chaco Canyon about which little is known.  Salmon, like Hungo Pavi, is an “E-shaped” great house, with a central room block on the north side and wings extending to the south at the east and west ends.  The whole thing seems to have been constructed as a single unit within a few years around 1090, which makes it by far the largest single building episode known in the Chaco system and has interesting implications for understanding why it might have been built.  There has long been a dispute over whether the outliers in the Chaco “system” represent direct colonization by people from Chaco, local emulation of Chacoan forms by emerging elites, or something else.  Reed supports a colonization model, but he sees the Chacoans who came up to Salmon and built the great house as having also brought local residents in to live there with them, and perhaps to work on building the thing too.  The local area seems to have lacked a substantial pre-Chacoan population, so it’s not entirely clear where these locals would have actually come from, but it does make sense that colonists from Chaco would have selected a relatively uninhabited location for their new settlement.

Anyway, back to the room suites.  Most of the site seems to have originally been laid out as a series of suites, each of which involved a large square room facing the plaza connected to three smaller rooms behind it.  The large square rooms seem to have been single-story, but the smaller rooms mostly had two or three stories.  The large square rooms especially tended to have many residential features such as hearths, and the smaller rooms often had features such as milling bins that also suggest domestic use.  There were also a few rooms that had very large milling bins, larger than would have been necessary for individual households, which suggests that site residents might have been grinding corn on a large scale.  This, combined with Salmon’s location in a fertile valley, in turn suggests that the site may have been founded partly or even primarily as an agricultural colony that would have exported corn and/or cornmeal to Chaco and perhaps other areas with poorer agricultural potential.  There is evidence from studies of corn at Chaco that much of it was imported from the Totah, which meshes nicely with this idea.

Backfilled Rooms at Salmon Ruin

The key thing here, though, is that it’s the large square rooms that seem to have been the primary living rooms.  This is similar to the case at some early room suites at Chacoan great houses, such those in the western wing of Pueblo Bonito.  Later great houses at Chaco seem to have largely either lost the room suite pattern or modified it beyond recognition, but at Salmon it stands out clear as day.

There’s something missing here, though.  Salmon (in the Chacoan period) was composed almost entirely of room suites made up of large square and small rectangular rooms.  But what about kivas?  These round rooms are often considered one of the hallmarks of pueblo architecture, and while their function is disputed their presence is often thought of as near-universal.  Salmon complicates this picture considerably.

Great Kiva, Salmon Ruins

There were two round rooms in the Chacoan-period construction at Salmon (note these caveats; they’re important).  One was the great kiva in the plaza, a standard Chacoan form that presumably had ritual functions, and another was and elevated, blocked-in kiva at the center of the main roomblock that Salmon specialists refer to as the “Tower Kiva,” although it actually isn’t a tower kiva in the sense in which Chaco specialists use the term.  Both of these seem to have had important community-wide functions and they were probably not residential (though I’m less sure of this in the case of the Tower Kiva than in the case of the great kiva).  What Chacoan-period Salmon lacked, however, were the smaller kivas that are ubiquitous at Pueblo Bonito, Chetro Ketl, and other great houses at Chaco.  These are the kivas that Steve Lekson thinks were residential rather than ceremonial, although others disagree.  In any case, they don’t seem to have been part of the original plan for Salmon.

So what gives?  Well, if we buy Lekson’s theory, which I basically do, what seems to be going on here is that the residential functions filled by kivas elsewhere were filled by the large square rooms at Salmon.  As I noted in the previous post, the fact that some great houses have room suites with big square rooms while others have different types of suites with associated kivas suggests that there were two different residential patterns in the Chacoan system that might correspond to some important dimension of social complexity.  Salmon seems to support this idea, in that it apparently was designed (and occupied?) by one of these groups rather than the other, whereas at Pueblo Bonito, at least, both seem to have been present.

Kiva 121A, Salmon Ruin

If you’ve been to Salmon, this may seem a bit confusing, because one of the most obvious things you can see there is that there are plenty of kivas!  They’re built into the square roomblocks, just like at Chaco!  And, indeed, they are.  Excavation showed, however, that these kivas are not original to the building.  Instead, they were built into the large Chacoan rooms in the post-Chacoan period.  The Chacoan period at Salmon seems to have ended around 1125 or 1130, coincident with the end of major construction at Chaco and extensive evidence of major changes in the Chaco system that may or may not have constituted the “collapse” of that system.  The original idea the excavators had was that this involved the total abandonment of Salmon for a few decades, after which it was reoccupied by a new group with ties to the Mesa Verde region to the north which remained there until the site was abandoned completely in the 1280s or 1290s along with the whole region.  It later became clear that there was at least a small “Intermediate” occupation between the “Primary” (Chacoan) and “Secondary” (Mesa Verdean) occupations, and the CDA project has redefined these occupations to emphasize continuity between the last two, seeing them as “early” and “late” periods of a continuous local “San Juan” occupation as opposed to a migration from the north.

In any case, it was the “Secondary,” “Mesa Verdean,” or “San Juan” occupants, not the Chacoans, who built kivas into the Chacoan rooms.  Note that architecturally, these are not Chacoan kivas, which have a very standardized set of features, but instead more closely resemble Mesa Verde kivas and may reflect local architectural traditions such as the use of river cobbles rather than sandstone blocks in some contexts.  They were mostly built into the large square living rooms, although some were in the smaller rooms, which were also often subdivided with adobe walls to create spaces more typical of small sites in the area than the large rooms typical of Chacoan great houses.

Kiva at Salmon Ruin Showing Use of Cobble Masonry

The fact that these kivas were mostly built into the Chacoan living rooms is another point in favor of Lekson’s arguments that kivas were residential, especially since there’s some evidence from the Salmon excavation data that there was more continuity between the “Chacoan” and “San Juan” occupations than the excavators thought.  One interpretation for the construction of the kivas is that whoever was living at Salmon in the 1200s knew how the room suites had been used in the Chacoan era and wanted to continue to use them the same way but in a way that was consistent with local traditions and practices.  These people may or may not have been descended from the original inhabitants of the site.

The upshot of this is that we have strong evidence here that there was a practice in at least one Chacoan great house in the late 1000s and early 1100s of residential use of room suites focused on large square rooms facing the plaza.  It’s hard to tell if this pattern holds for any of the sites at Chaco itself (Hungo Pavi?), since the most extensively excavated ones were excavated long before the techniques that allowed the Salmon excavators to carefully differentiate between occupations were developed.  There is some evidence from the less extensive excavations at Pueblo Alto, however, which were done by the Chaco Project around the same time Salmon was being dug, that there was a similar pattern there of kivas being added to an original plan lacking them.  The kivas in the southeast corner of the Chetro Ketl plaza also seem to be very late, and the other parts of that site have relatively few kivas, most of them in elevated contexts similar to the “Tower Kiva” at Salmon.  Something similar may be true for the blocked-in kivas in the central roomblock at Pueblo del Arroyo.

Chacoan Masonry at Salmon Ruin

That leaves Pueblo Bonito.  The enormous complexity and early excavation of this site make teasing apart the different stages of construction enormously difficult, but one possibility is that at least some of the kivas there have a similar history to the ones at Salmon.  This may be particularly the case in the southwest corner, which has several kivas that may have been added into older square rooms and is also the area with the well-defined early room suites with large square rooms taking the place of kivas.  It’s also likely that many of the plaza kivas were very late additions like the ones at Chetro Ketl.  The blocked-in kivas in the southeast corner are trickier to interpret, and I’m not sure at this point if they represent something like the Salmon pattern or a different phenomenon entirely.

The excavations at Salmon resulted in a vast amount of information that is only now beginning to be incorporated into the study of the Chacoan system overall.  This evidence for residential use is just one example, but an important one, of how this data can lead to important insights not just about Salmon itself but about other parts of the Chaco world as well.

Central Roomblock at Salmon Ruin

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What Makes a “Kiva” “Chacoan”?

Entrance to Kiva at Edge of the Cedars State Park, Blanding, Utah

Sticking with the topic of the small round rooms traditionally called “kivas,” which Steve Lekson would prefer to call simply “round rooms,” it’s important to note that there is a wide variety of formal types.  In addition to the modern distinction between square and round kivas, which is basically geographical with square ones in the western pueblos and round ones in the eastern pueblos, and setting aside the highly specialized “great kivas,” among the prehistoric kivas (I’m going to stick with the traditional term for now) of the San Juan Basin there are at least two types.  In his writings on Chacoan architecture, Lekson has distinguished between two main types of kivas found in great houses at Chaco: “Chacoan” and “Non-Chacoan.”

Kiva Z, Pueblo Bonito

The type of kiva that Lekson defines as “Chacoan” (originally defined by Neil Judd, who excavated Pueblo Bonito and Pueblo del Arroyo in the 1920s) has a variety of standard features, especially in the later examples from the period of approximately AD 1075 to 1130 when the Chaco system was at its height.  They are not quite as standardized as Chacoan great kivas, but the features associated with them are nevertheless found wherever there is evidence for Chacoan influence during this period, and it seems clear that this particular suite of features is a specifically Chacoan development.  (These kivas have often been called “clan kivas” in the past, but I don’t like that term because of the huge assumptions it makes about social organization and kiva function, so I’m just going to call them “Chacoan kivas.”)  The standard features defined by Judd are:

1. A central firepit
2. A subfloor ventilation system with an opening south of the firepit leading to a shaft opening south of the kiva
3. A subfloor “vault” west of the firepit
4. A bench around the circumference of the kiva
5. 6 to 10 low “pilasters” roughly evenly spaced around the bench
6. A shallow recess in the bench at the southern end

Lekson adds two more features, which are certainly present in many Chacoan kivas but less universal than Judd’s and more controversial:

1. The elevation of the kiva into an aboveground square enclosure
2. “Wainscoting” around the edge of the bench

This set of features is certainly consistent with the general “San Juan” type of kiva that developed out of the Basketmaker pithouse, but it differs from the kivas found most commonly in areas like Mesa Verde to the north in a few ways.  Before going into the differences, though, I want to just explain the importance of the lists of features given by Judd and Lekson.

Kiva Firepit at Lowry Pueblo in Colorado

Firepit: All kivas have firepits; it is one of the defining characteristics of the form.  In Chacoan kivas specifically, the firepit is offset slightly to the south of the center point of the kiva, which is always circular.  Firepits in Chacoan kivas are deep, circular or square in plan, and usually lined with masonry.

Subfloor Ventilation Shaft in Kiva at Edge of the Cedars State Park, Blanding, Utah

Ventilation System: One major characteristic of San Juan small kivas in general is that they have ventilation shafts, usually at the southern end.  Jesse Walter Fewkes wrote an article in 1908, which I mentioned in an earlier post, in which he set forth an argument that these shafts were indeed for ventilation rather than for any other purpose, and this argument is now more or less universally accepted.  There are different types of ventilation system, however, and this is one of the major features distinguishing Chacoan kivas from other types.  Chacoan kivas have ventilation shafts that run underneath the floor of the kiva and are accordingly called “subfloor” ventilation shafts.  One end of the shaft opens vertically into the floor just south of the firepit, and there may or may not be a slab or low wall in between used as a deflector to distribute the air and shelter the fire.  From this opening the shaft runs down a short distance then turns and runs horizontally to the south underneath the floor (or as a shallow trough that would have been covered by boards or poles) until it gets past the southern wall, at which point it turns again and runs vertically upward until it reaches the ground surface (at the level of the kiva roof, but just to the south of it) and opens up to provide the source for fresh air.

Great Kiva at Chetro Ketl Showing Floor Vault

Floor Vault: Most Chacoan kivas have a single rectangular “box” sunk into the floor just to the west of the firepit.  These are often filled and plastered-over, and sometimes have boards covering them, so Lekson notes that this feature may actually be more widespread than it appears from the literature (since excavators may have missed covered vaults in some cases).  Since about three-quarters of excavated Chacoan kivas had evidence of vaults, this suggestion implies that these may have been nearly or literally universal in actual fact.  These vaults are reminiscent of the similar “vaults” known from Chacoan great kivas, although its unclear why there would be different numbers of them.  In both great and small kivas the function of the vaults is obscure.  The fact that they sometimes have wooden boards on them has led some to argue that they were “foot drums” that people would have danced on to create a drumming sound, but Lekson points out that they are often filled with sand, which makes this explanation implausible.

Chacoan Kiva at Aztec Ruins National Monument

Bench: There is a low masonry bench around the circumference of the room.  This is another standard feature of San Juan kivas in general, although the bench is not always made of masonry in non-Chacoan versions.

Kiva Pilasters at Pueblo Del Arroyo

Pilasters: At roughly equal intervals around the bench there is a series of “pilasters.”  This term comes from Mesa Verde kivas where the pilasters are often tall and made of masonry, and it is not as applicable to Chacoan kivas where the defining feature of a “pilaster” is a short segment of a wooden log oriented radially with one end set in the wall just above the bench.  These beams are often set in small masonry cubes which do somewhat resemble Mesa Verdean pilasters and imply a similar function.  Mesa Verdean pilasters typically serve to support a cribbed roof, and Chacoan pilasters have often been interpreted similarly, although Lekson disagrees with this interpretation.  The issue of roofing is discussed more fully below under “wainscoting.”

Kiva I at Pueblo Bonito Showing Southern Recess

Recess: At the south end of the bench there is a shallow “recess” in which the bench narrows.  The location of the recess corresponds to the location of the subfloor vent shaft, but since the vent shaft is underground it does not actually have anything to do with the recess (this is another difference from Mesa Verdean kivas, which have above-floor vent shafts that open into the recess, which is often more prominent).  There is some evidence that at least in some cases there may have been a shelf over the recess, which would have continued the line of the bench and created a large niche under it.  The purpose of this recess is obscure.

Southern Recess in Kiva at Pueblo del Arroyo

Those are the criteria Judd gives, and they are pretty universally accepted and uncontroversial.  Lekson adds two more, which are a bit more controversial.

Corner of Room Containing Blocked-In Kiva at Tsin Kletzin

Elevation and Blocking-In: The early examples of Chacoan kivas at Chaco great houses, dating from around AD 900 to 1070, are generally subterranean and usually located in the plazas of great houses, backed by suites of rectangular rooms.  The “classic” examples of Chacoan kivas, dating from about 1075 to 1130, are generally built into square rooms within the great-house roomblocks, usually on the first floor but occasionally on the second.  Lekson considers this tendency to “block-in” kivas a key part of the Chacoan kiva tradition, and in his 2007 chapter on great house form he goes into some detail on the historical development of the Chacoan kiva, starting with the early tenth-century examples, which are poorly known, and continuing through what he refers to as “transitional” Chacoan kivas, built between 1030 and 1070, only a few of which have been excavated.  The best known of these is Kiva G-5 at Chetro Ketl, which was later covered over by later kiva construction culminating in an elevated “classic” Chacoan kiva (Kiva G) but is still kept open and visible underneath the later construction.  These transitional kivas had most of the characteristics of later elevated kivas, and by Judd’s standards they would all be considered just Chacoan kivas.  Lekson makes a big deal about the blocking-in, however, and it is true that this is something that markedly distinguishes Chacoan kivas from other types.  No one else did this, and it’s very odd in a structural sense since those huge masonry cylinders needed extensive support, which often meant the “interstitial” rooms in the corners of the square room were braced with timbers or filled in with earth.  One problem with using this as a defining characteristic of Chacoan kivas, though, is that there are a few late, very large Chacoan kivas that are subterranean and located in plazas rather than being blocked-in.  These approach great-kiva size, but they lack the features of great kivas.  The best known of these is the Court Kiva at Chetro Ketl, which was later remodeled into a great kiva.  Only two other examples have been excavated, Kiva R at Pueblo Bonito and Kiva J at the Talus Unit.  Kiva R has standard Chacoan kiva features, whereas Kiva J was only partially excavated and little is known about its features.  Five additional kivas like this are known at Pueblo Bonito, and Lekson describes them as unexcavated, although at least two or three of them clearly seem to have been excavated as far as I can tell and they seem to have typical Chacoan kiva features, so I’m not sure what Lekson’s talking about when he says they’re unexcavated.  Indeed, one of these, Kiva O, is still visible in the east plaza.  (Kiva R, which is in the west plaza, is also visible.)  The fact that some of the largest Chacoan kivas are subterranean and in the plazas of great houses rather than elevated and blocked in makes Lekson’s use of blocking-in as a standard attribute of Chacoan kivas problematic, even just looking at the “classic” Chacoan kivas built after 1075.

Kiva L, Pueblo Bonito

Wainscoting: This is the most controversial of Lekson’s criteria for Chacoan kiva status.  Basically, many of the excavated Chacoan kivas have a series of thin wooden poles (or, less often, boards) rising from the back of the bench and leaning in toward the center of the ceiling.  Between them is a sort of wickerwork held together with clay or adobe (i.e., a sort of wattle-and-daub or jacal), plastered with mud on the interior side.  The space behind this wickerwork is either left open or filled in with trash or other vegetal material (Lekson’s account is unclear here).  Lekson claims that this “wainscoting,” supported by the poles, formed the ceiling of the kiva, sort of a false dome, with the exterior roof at the top being supported by horizontal beams much like those used in the roofing of standard square rooms.  This is in contrast to the standard way that Mesa Verde kivas were roofed, which was also a false dome but one made of cribbed logs beginning on the pilasters and alternating rows up to the roof.  (This is the way Navajo hogans are traditionally roofed as well.)  Some examples of intact roofs like this are reported in the Mesa Verde region, including one at Square Tower House that Fewkes used as the basis for interpreting and reconstructing the roofs of kivas at Spruce Tree House, which had not survived intact.  There is at least one kiva at Pueblo Bonito that also had a largely intact cribbed roof (Kiva L).  It has often been assumed that most Chacoan kivas, including the blocked-in ones, also had cribbed roofs resting on the pilasters, but it’s noteworthy that Kiva L is not blocked-in, although it does otherwise show classic Chacoan features, and that Kiva 67, another plaza kiva with classic Chacoan features, also showed evidence of having a cribbed roof through the impression of a log in clay spanning two pilasters, although the log itself did not survive.  It’s possible, then, that the development of “wainscoting” as a means to roof kivas was an innovation spurred by the building of kivas in square rooms, which could easily be given flat roofs like other square rooms, although it’s not really clear what the advantage of wainscoting over cribbing would have been.  It would probably have used less timber, but the Chacoans were hardly averse to importing huge quantities of timber and it’s hard to see them making decisions about architecture based on efficient use of resources.  Chacoan kiva roofing remains an open question.

Cribbed Kiva Roof at Edge of the Cedars State Park, Blanding, Utah

Kivas are particularly vulnerable to deterioration if they are left open to the elements, so all of the small kivas at Chaco that have been excavated have been subsequently backfilled to varying degrees.  Many have been filled entirely, so that no trace of them remains on the surface; this is the case with the Court Kiva at Chetro Ketl and many of the plaza kivas at Pueblo Bonito.  Others have only been refilled partly, in some cases to a low level so that the bench and pilasters are still visible and in other cases to a higher level so that only the upper parts of the wall can be seen.  Thus, there is nowhere at Chaco where the floor features of a Chacoan kiva can be seen.  This is in contrast to Mesa Verde, where especially at the cliff dwellings like Spruce Tree House many well-preserved kivas in sheltered locations have their floors open to be examined.   Those are generally Mesa Verde-style kivas, of course, rather than Chacoan ones.  The best example I know of a basically Chacoan small kiva where the floor features can be seen is the reconstructed blocked-in kiva at Edge of the Cedars State Park in Blanding, Utah.  This is an outlying great house that is much more modest than what you see at Chaco, but one of its kivas has been given a restored cribbed roof and other reconstructed elements to give a sense of what it would have likely looked like in its prime, and as it happens this kiva shows most elements of the Chacoan style despite being far from Chaco itself and in the Mesa Verde region.  Also in the same region, one of the kivas at Lowry Pueblo has not been totally reconstructed to the same extent but it does have a protective roof over it and so also has its floor features open.  This is another blocked-in kiva at an outlier far to the north that is nonetheless a good example of classic Chacoan kiva design.

Fewkes, J. (1908). Ventilators in Ceremonial Rooms of Pre Historic Cliff-Dwellings American Anthropologist, 10 (3), 387-398 DOI: 10.1525/aa.1908.10.3.02a00020

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A Virtual Tour of Pueblo del Arroyo

Pueblo del Arroyo Sign

Pueblo del Arroyo, the latest and smallest of the large “Bonito-style” great houses in Chaco Canyon, is an interesting site for a variety of reasons.  It occupies a transitional place in the history of the canyon, both between the Bonito phase and the succeeding McElmo phase and between the era of the Chaco system as a whole and whatever it was that succeeded it.  Although it was built later than many other large sites in the canyon, and thus had a shorter period of overall occupation, it still shows a considerable amount of change over time that illustrates larger-scale changes that are not as visible at the older, more complicated sites such as Pueblo Bonito.

Northwest Corner of Pueblo del Arroyo

The northwest corner of Pueblo del Arroyo is the first part of the site one reaches when walking up from the parking lot.  This part of the site, the north wing, is unexcavated, and it offers a good opportunity to see what the rest of the sites looked like before excavation.  There are a considerable number of standing walls, showing the overall size and shape of the building, but most of the lower stories, especially the first story, are still mounded over with windblown sand.  This sand, which filled in the lower stories which were protected by thick walls and prevented from falling down like the upper stories, still protects whatever lies inside these rooms in the north wing.  We don’t know what is in them, but judging from what was found in the rooms elsewhere that have been excavated, it’s probably pretty impressive and well-preserved.  This sand, which protects the contents of the rooms very well, is one of the things that makes Chaco such a well-known and spectacular place: in addition to the fineness of the architecture, the artifacts preserved by the sand are quite impressive as well.

View of Pueblo del Arroyo from Its North Wing

Moving along the west wall of the site and up into the north wing, one can see pretty much the whole site.  In contrast to the larger sites like Pueblo Bonito, Pueblo del Arroyo is a lot easier to get a handle on.  It’s small enough for the whole thing to be readily visible from the upper parts of the north and south wings.

Latilla Holes at the Oldest Section of Pueblo del Arroyo

The earliest construction stage at Pueblo del Arroyo took place between around 1065 and 1075 AD.  This was the back portion of the central roomblock, starting with the west wall.  It was three rows wide and approximately the same length as the final central roomblock, although some parts may have been covered over by later construction of the wings.

Later, between about 1095 and 1105 AD, two wings were added to this roomblock, one on the north side and one on the south side.  These are pretty similar to each other, although they differ in a few ways.  They both consist of one or two central elevated round rooms surrounded by rectangular rooms to form an overall rectangular shape.

Kiva Pilasters at Pueblo Del Arroyo

The north wing, which originally went up three stories, has two round rooms at its center, one on the second-story level and one on the third.  The one on the third story has been excavated and is the only part of the north wing to be excavated.  It is a good example of a “Chacoan” style round room (or “kiva”), with an encircling bench containing several pilasters, cube-shaped masonry blocks with radial logs inside them.  The function of the logs is obscure, but the pilasters as a whole served as bases for the logs that were laid across them and then built up to form a cribbed roof, sort of a false dome with a smoke hole in the center that also provided access to the room via ladder.  As the presence of a smoke hole implies, there was also a hearth on the floor of the room (now covered up in this case, like the other floor features, by backfill).  On the south end of the room is a vent shaft, which brought in air from outside and could open either at the level of the bench or through the floor.

In addition to the internal features, the main thing that distinguishes “Chacoan” round rooms from others is their positioning within the site.  Unlike many other round rooms, which are subterranean or semi-subterranean, these rooms built above-grade into the square roomblocks around them.  This is a distinctive feature of Chacoan sites, but it’s pretty mysterious.  It’s totally impractical structurally, as it creates four small corner rooms that are generally pretty useless and, indeed, are usually used to buttress the round room, either with logs set across them or by being filled in entirely.  Whatever the purpose of the blocking-in, however, it is a typical feature of Chacoan sites.

Bonito-Style Masonry atop McElmo-Style Masonry, Pueblo del Arroyo

Another more unusual feature of this particular round room can be seen where the fill has been cut away to reveal a lower level of masonry below the main bench level.  This masonry is quite different from the fine “Bonito-style” masonry above it, which uses the hard, tabular sandstone quarried on top of the mesas that is typical of the masonry in Bonito phase great houses.  Instead, it is made of larger blocks of the soft, yellowish sandstone found at the base of the cliffs.  It resembles the “McElmo-style” masonry seen in the construction of sites such as Kin Kletso, which is quite close to Pueblo del Arroyo and visible from the north roomblock.  These sites seem to have been built in the early 1100s, toward the end of the Chaco era, and their style is therefore generally thought of as later than the “classic” Bonito style.  Pueblo del Arroyo, however, was built over a period that seems to been transitional between the two styles, and the north roomblock especially shows several places where Bonito-style and McElmo-style masonry seem to have been used at the same time, often, as in this round room, with the “later” McElmo masonry below the “earlier” Bonito masonry, clearly showing that McElmo masonry is not necessarily later than Bonito masonry at all.  Explaining this is difficult, and Pueblo del Arroyo seems to be the only site that shows this sort of thing on this scale.

Burned Kiva at Pueblo del Arroyo

The south wing, unlike the north, has only a single blocked-in round room at its center, at the second-story level.  This room is larger than either of the two round rooms in the north wing, but it is otherwise pretty similar to the excavated one there.  The south wing as a whole is also pretty similar to the north wing, except that it went up four stories instead of three.  Both wings consist of a very regular pattern of square rooms surrounding one or two round rooms, which is a pattern very similar to that seen in the later McElmo sites, which are very regular and modular and tend to be made of one or more “units” consisting of one or two round rooms surrounded by square rooms.  (Most McElmo sites have one of these units; Kin Kletso has two.)

Kin Kletso

The two wings of Pueblo del Arroyo, then, both built around 1100, are strikingly similar in plan to the McElmo units of a few years later.  They are generally still made of Bonito-style masonry (although note what I said above about the overlap in styles), but otherwise seem to be precursors of the later sites.  Again, hard to explain, but seemingly unique to this transitional site.

Partial Roof at Pueblo del Arroyo

Another difference between the north and south wings is that the south wing has been excavated, so it is possible to look down from the level of the elevated round room and see quite a bit of the lower stories.  They have been refilled to varying levels, but there is still quite a bit to see, including, in one room, some of the original roof beams showing the style of roofing, which consisted of large beams of ponderosa pine spanning the short axis of the room, crossed perpendicularly above by smaller beams of aspen or other small trees, then covered with juniper splints which sealed in the packed earth that formed the floor of the room above.

Plaza-Facing Rooms at Pueblo del Arroyo

The next stages of construction are harder to date, but they seem to have taken place sometime in the early 1100s.  They are the expansion of the central room block eastward toward the plaza, with the new construction consisting largely of blocked-in round rooms at various levels, and the final enclosure of the plaza within a one-story arc of rooms, forming an overall D-shape to the building.  This shape is quite common for Bonito phase great houses, and it is seen in Chetro Ketl, Pueblo Alto, Hungo Pavi, and a variety of other sites as well.  Interestingly, the sequence of construction of all these sites seems to have been the same as well, starting with the central roomblock, followed by the two wings, then finishing with the enclosing arc of rooms.  This is the case even though the sites were all begun and finished at different times, which implies that they may all have been planned with the final shape in mind from the very beginning.

Despite its rather typical shape and sequence of construction, however, Pueblo del Arroyo is unlike any other great house in the canyon in its positioning and orientation.  While most of the great houses are at the foot of the cliffs on the north side of the canyon and face south, with their highest levels on the north side and the rooms terracing down from there to the enclosed plaza on the south, Pueblo del Arroyo is out in the middle of the canyon, right next to the Chaco Wash (hence its name), and it faces east, with its long, straight back wall with the highest stories on the west side and the enclosed plaza on the east.  This is very difficult to explain.  It could have something to do with its late date, but it’s clearly not the case that there was no room left on the north side of the canyon at the time Pueblo del Arroyo was initially constructed, since Kin Kletso, which was constructed even later, is right at the foot of the cliff quite close to the site of Pueblo del Arroyo.

Kin Kletso from Pueblo del Arroyo

One reason Pueblo del Arroyo might have been placed as it was is apparent from a look at the south side of the building, which is interesting for many reasons.  Like many exterior walls of great houses, this one has no doorways on the first floor but does have several doorways on the second floor (and probably on the third and fourth, which have not survived high enough to tell).  Some of these doorways are T-shaped, an unusual and probably significant shape that has been proposed as a sign of Mesoamerican influence, while others are more typical rectangles.  It may seem a bit odd to have doorways on the upper stories when there are none at ground level, but the reason is actually fairly clear from evidence at other sites such as Chetro Ketl, where there were balconies at the floor levels of the second and third stories on the outside of the building.  Although there is no direct surviving evidence for balconies at Pueblo del Arroyo, it is reasonable to conclude that there were originally balconies and that the upper doorways didn’t serve as entrance points to the building but as exit points from the building to the balconies.

T-Shaped Doorway at Pueblo del Arroyo

If there were balconies on the south side, though (which, remember, is not the front of the building), what were they there for?  What would people see when they walked out onto the balconies?

The answer is clear from turning around and looking south, where a couple of potentially important things are clearly visible.  The first, of course, is the wash, which runs right next to Pueblo del Arroyo.  Keeping an eye on the water flow would be a useful thing to do, for obvious reasons.  The second is perhaps a bit less obvious in its importance, but it’s at least as striking in its effect.  This is the large gap in the mesa to the south directly across from Pueblo del Arroyo.

South Gap from Pueblo del Arroyo

This gap, called South Gap, was one of the three main entrance points to the canyon from the south, and it makes sense that having a building overlooking it would be useful both for monitoring who and what was coming in and for impressing people entering the canyon with the monumental nature of the building.  The early great houses built in the 800s, Pueblo Bonito, Una Vida, and Peñasco Blanco, are all built at or near the gaps (respectively: South Gap, Fajada Gap, and the point to the west where the mesa ends, which is not really a gap but is still an entrance point to the canyon), but Pueblo Bonito is not actually directly across from South Gap.  Pueblo del Arroyo is.  It is hard to escape the conclusion that the odd siting and orientation of Pueblo del Arroyo likely had something to do with this.

Pueblo del Arroyo from South Gap

There’s another odd thing about the south side of Pueblo del Arroyo.  When the south wing was initially constructed, the second, third, and fourth stories of the southernmost row part of the addition were constructed as usual, with long walls subdivided by cross-walls to form a series of rooms.  On the first story, however, there were no cross-walls.  The whole thing formed one extremely long, continuous room.  As a result, the weight of the upper stories was not adequately supported, and the wall began to lean outward.  To stabilize it the builders put up a series of buttresses on the outside, which seem to have worked, and the wall is still standing and in fairly good condition today.

South Addition to Pueblo del Arroyo

Much later (although it’s impossible to say exactly when), someone (it’s impossible to say exactly who) came along and turned these buttresses into the cross-walls for a series of rooms built along the south wall of Pueblo del Arroyo using very crude masonry.  These rooms show lots of evidence of residential use, so we do know what the people were doing in them, but beyond that it’s very difficult to say why they built them.  They do seem to have used at least some rooms inside Pueblo del Arroyo as well, so it wasn’t that they didn’t have access to the building.  This was likely long after the fall of the Chaco system,  probably in the late 1100s or even later, and it’s a good example of the changes that took place in the canyon after the end of its regional importance.  For some reason these changes are much more apparent here at Pueblo del Arroyo than at other sites.

Modern Erosion-Control Measures in Chaco Wash at Pueblo del Arroyo

Walking around the southwest corner of the building, one can see just how close the wash comes to the building.  There are a variety of erosion-control devices visible to keep the wash from eating away at the building any more than it already has.  There are also many preservation measures apparent to drain water away from the building and into the wash, most notably a downspout and pipe that the preservation crew painted to blend in with the surrounding masonry.  It’s one of their more whimsical efforts.

Drainage Pipe at Pueblo del Arroyo, Painted to Blend In

Perhaps the most spectacular example of the post-Chacoan changes at Chaco that can be seen at Pueblo del Arroyo is on the west side.  Built right against the back wall of the building is a remarkable and mysterious structure built of three concentric circular masonry walls, with the two outer rings divided into rooms by radial walls.  The masonry style indicates that at least most of this structure is clearly later than the rest of the building, being more like the classic McElmo style of the early to mid-1100s.

Tri-Wall Structure at Pueblo del Arroyo

This is an example of what is known as a “tri-wall structure.” It’s the only one at Chaco, but not the only one anywhere.  They are mostly associated with the area to the north of Chaco, which was rising in importance regionally during the 1100s at the same time that Chaco was declining.  There are tri-walls in the Mesa Verde area, and they are particularly associated with the Totah area along the middle San Juan river valley.  There are at least three of them at Aztec Ruins, which seems to have become a major regional center around this time.  This one at Pueblo del Arroyo, then, seems to indicate influence from the north in the post-Chaco area, although beyond that it’s hard to say much about it.  It has been excavated (and later backfilled for preservation), but the excavations found that it had been substantially dismantled in antiquity, apparently for building stone.  It’s not clear where the stone was used, but the row of rooms along the south side of Pueblo del Arroyo is one obvious possibility.

Hubbard Tri-Wall Structure at Aztec Ruins National Monument

Because of the disassembly, not much was left to indicate the function of the tri-wall.  Despite its round shape, however, it bears little resemblance to other round rooms such as great kivas.  Most other round rooms of whatever size and shape have hearths in the center, but the tri-wall doesn’t.  Instead, the innermost circle has a flagstone floor.  This is a very unusual feature, as rooms in these sites almost always have earthen floors, but it is known from some other sites where it seems to be a functional aspect of storage rooms used to keep rodents out.  Here, however, it likely has some more esoteric purpose.

The prevalence of tri-wall structures throughout the San Juan basin during the 1100s, and their absence before and after, seems to indicate that they were associated with a short-lived flourishing in the immediate post-Chaco era of some sort of regional social or ceremonial system, possibly centered on Aztec.  Since it was so short-lived, however, and no aspect of it seems to have survived in recognizable form into the present-day Pueblos, it is perhaps even harder to interpret than the Chacoan system that it seems to have replaced.

West Wall of Pueblo del Arroyo Showing Addition Associated with Tri-Wall Structure

Coming back around from the tri-wall to the northwest corner, one has circled the entire building.  It is notable that the tri-wall, one of the later, mysterious additions that make Pueblo del Arroyo so interesting, is right up against the west wall, the earliest part of the building, which in a sense brings things full circle.  Despite its relatively short period of occupation, Pueblo del Arroyo shows a lot of change and mystery, which makes it a fascinating place deserving of much more attention than it usually gets.

View from Doorway at Pueblo del Arroyo

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