Archive for the ‘Palynology’ Category

Sleeping Ute Mountain and Surrounding Landscape from Four Corners

If you stand at the Four Corners monument and look in the direction of Colorado you will see Sleeping Ute Mountain dominating the view.  From this direction you are looking at the southwest side of the mountain, and in front of it you see the southern piedmont.  On the right side of the piedmont, though not visible from this distance, is Cowboy Wash.  It’s one of several ephemeral streams running from the mountain itself across the piedmont to the San Juan River.

One thing that might strike you about the view from this perspective is that it looks like an awfully dry, desolate, uninhabitable wasteland.  And you would be correct to think that.  The southern piedmont of Sleeping Ute Mountain is an extremely arid and inhospitable environment even by the standards of the Southwest, which is saying something.  It’s only a few miles from Mesa Verde to the east and the Great Sage Plain to the north, both areas that get relatively abundant rainfall and supported large and prosperous prehistoric communities, but it is worlds away from them environmentally.  While those areas get sufficient rainfall to support dry farming, and the Great Sage Plain is commercially farmed even today, the southern piedmont does not, and any type of agriculture there would have to rely on some sort of irrigation.  Today the Ute Mountain Ute tribe has a large irrigation project in the area, using water brought in from McPhee Reservoir, 45 miles to the north, via the Towaoc Canal.  The construction of the reservoir and the canal was part of the Dolores Project, which involved substantial archaeological excavation of the inundated area that significantly improved archaeological understanding of the prehistory of the region.  This work took place from 1978 to 1985 and was known as the Dolores Archaeological Project, the largest salvage archaeology project in US history.

McPhee Reservoir, Dolores, Colorado

The creation of the irrigated fields on the piedmont resulted in further salvage excavations in the 1990s.  Among the sites excavated was 5MT10010, which contained considerable evidence of a gruesome incident of probable cannibalism around AD 1150.  It is not the only site in the area to show evidence of cannibalism during this period; in fact, three other sites in the same community, excavated slightly earlier in connection with the construction of the canal, also showed evidence of having been destroyed in an incident involving extensive processing of human remains in a way suggesting cannibalism, and there are several other sites in the area showing similar assemblages, most from the same period but at least one from a later period.  It is at 5MT10010 that the most solid evidence for actual cannibalism, as opposed to processing of bones in a way that may or may not indicate actual consumption of human flesh, in the form of a coprolite that tested positive for the presence of human muscle tissue.

There are many questions that arise from these findings, but one of the most puzzling is also one of the simplest: what were people doing living at Cowboy Wash in the first place, and how did they manage it?  After all, they weren’t building giant dams and canals of the sort involved in the Dolores Project.  In many parts of the Southwest, especially upland areas like Mesa Verde, dry farming using only rainfall was standard during this period, and water control techniques were generally used only for domestic water if a nearby spring or other reliable source was not available.  There are a few springs on the southern piedmont that probably would have supplied sufficient domestic water for the small number of people living there, but the rainfall would definitely not have been sufficient to farm with.  The only source of water at all sufficient for agriculture would have been the occasional floods, from spring snowmelt and summer thunderstorms, that would flow through Cowboy Wash itself and the other drainages on the piedmont.  None of these flows permanently today, and there is no evidence that they ever did.  As at Chaco Canyon, then, which is similarly dry, farming would have to have been based on some sort of technique for capturing the floodwater.

Flowing Chaco Wash and Cliffs below Peñasco Blanco

There are a variety of ways this might be done, including diverting the rainwater from cliffs, as was done at Chaco, planting along the sides of the drainage where the floods would regularly overflow the banks, and what is known as “ak-chin” farming, as practiced by the O’odham of southern Arizona, which involves planting right in the path of the runoff at places where the velocity of the water is relatively low, as at the mouths of tributaries to main arroyos.  There are no sheer cliffs on the southern piedmont like the ones at Chaco, so probably a mix of overbank and ak-chin farming would have been practiced at Cowboy Wash.

A paper by Gary Huckleberry and Brian Billman addresses the nature of farming at Cowboy Wash, and also addresses a related issue, which is whether periodic entrenchment of arroyos due to drought played a role in the patterns of abandonment and migration that characterize Southwestern prehistory.  It is pretty clear by now that the paleoclimatological record shows periods of drought corresponding to periods of abandonment of certain parts of the Southwest, and one proposed mechanism for how this would have worked is that drought would have led to increased erosion and/or hydrological changes in the water table that led to the entrenchment of arroyos, which would have been disastrous for populations dependent on certain types of floodwater farming (especially overbank), as the broad floodplains of the local drainages would have been replaced by deep channels that took the water away quickly instead of letting it overflow to water the crops.  Ak-chin farmers would not necessarily have been affected to the same degree, but if the side drainages they used became entrenched as well they would not have been able to use their techniques either.  Thus, drought would lead to arroyo-cutting, which would lead people to leave formerly productive areas for others that were less affected.  This theory has been proposed as an explanation for certain events at Chaco, with the idea being that some of the social changes late in the Chacoan occupation were due to degradation of the Chaco Wash and the need to change agricultural strategies.  The phenomenon of arroyo-cutting in general is richly illustrated in historic times at Chaco.  The early reports of the Chaco Wash from the nineteenth century indicate that it was a shallow, meandering drainage, much like the current condition of the Escavada Wash to the north and the “Chaco River” that is formed by the confluence of the two at the western end of the canyon and flows north to the San Juan.  By the early twentieth century, and accelerating since then, however, the Chaco Wash through the canyon has cut down significantly and there is a very deep arroyo channel apparent today.

Entrenched Arroyo at Chaco

The drought-downcutting-abandonment theory makes sense as far as it goes, but as Huckleberry and Billman point out there are some problems.  For one thing, the extent to which arroyo-cutting is actually linked to drought, rather than other factors including the specific geology of the area, is hotly debated and there is no consensus.  The idea that while drought may be one factor causing arroyo-cutting there are other factors involved as well is supported by the fact that in different drainages in the Southwest that have been studied in depth the periods of arroyo-cutting do not necessarily correspond to region-wide droughts or other climatic changes.  In some areas they do, but in other areas they don’t.  At Cowboy Wash specifically, the available evidence indicates that the wash began to entrench sometime before AD 950, and that it began to refill with sediment sometime between AD 1265 and 1400.  If abandonment does in fact correspond to arroyo-cutting, then presumably the Cowboy Wash area should have been abandoned between 950 and 1265, and possibly occupied before and after this.  If downcutting results from drought, there should also be evidence of drought during the 950 to 1265 period.

The basic upshot of the Huckleberry and Billman paper is that neither of these expectations is met.  The evidence for drought conditions at Cowboy Wash generally matches that for the rest of the region, with the major droughts in the mid-twelfth century and late thirteenth century AD and several smaller droughts at irregular intervals before then.  This doesn’t show any particular relationship to the stratigraphic evidence for arroyo-cutting, which seems to have been going on to some degree throughout the period from AD 950 to at least AD 1265.  Furthermore, the evidence for settlement doesn’t line up either.  The marginal nature of the Cowboy Wash area implies that it would probably not have been occupied for most of prehistory, and this was indeed the case.  There were a few ultimately unsuccessful attempts to colonize the southern piedmont, however, and they don’t show any particular relationship to the periods of arroyo-cutting (although they do perhaps relate to periods of drought).  The first agricultural occupation of the area came during the Basketmaker III period, when a few pithouses were apparently used seasonally as summer fieldhouses, presumably associated with nearby fields, from about AD 600 to 725.  After these were abandoned, at a time which may correspond to a drought, the area does not seem to have been occupied again for more than three hundred years.  Then, around AD 1050, a few permanent, year-round sites were built.  These seem to have been occupied for only a few years, however, as there was no significant buildup of trash associated with them.  After they were abandoned, three larger villages, including one at Cowboy Wash, were established around AD 1075.  These had extensive trash deposits and seem to have been occupied for one or two generations.  These communities were apparently abandoned, however, when the next occupation began in the 1120s by a population with apparent links to the Chuska Mountain area to the south.  This occupation at Cowboy Wash is the community that was apparently destroyed around AD 1150 (again coincident with a major drought) when its inhabitants were mutilated and cannibalized.  After this event, the area was once again abandoned until about AD 1225, when two new communities were founded, including one again at Cowboy Wash.  Within a few decades the population at Cowboy Wash appears to have aggregated at Cowboy Wash Pueblo, following a typical pattern for the region.  Also typical of the region, the whole southern piedmont seems to have been abandoned by AD 1280, at the time of the “Great Drought” that coincides with major changes throughout the Southwest.

Entrenched Chaco Wash from Cliff Top near Pueblo Bonito

So basically, all of the attempts at year-round occupation of the southern piedmont seem to have occurred during the period that Cowboy Wash was being downcut.  While these were all ultimately unsuccessful, some lasted for a few decades, so clearly they were able to grow some food at some times.  This strongly implies that at least in this case, arroyo-cutting was not particularly linked to abandoned, although drought probably was.  Huckleberry address the issue of how farming could have been done during periods of downcutting by looking at Cowboy Wash and its tributaries today.  They find that while some portions of the main wash, especially, are indeed heavily downcut, other portions are not, and they label this type of drainage a “discontinuous ephemeral stream,” which is to say, a normally dry wash with some portions that are severely downcut and others that are not.  On the uncut portions, which include much of the length of the tributaries, overbank or ak-chin farming could easily be done today, and this was presumably the case in antiquity as well.  The hydrology of the area is such that the areas of downcutting would not have been stable, and would have tended to migrate upstream, but the complexity of the system is also such that this would not have made the entire system unusable; while some parts were being newly cut, others would be filling in, and prehistoric farmers would merely have to move their fields around a bit rather than abandoning the area entirely.

All that being said, however, the question of why people were trying to settle this quite harsh and difficult area in the first place.  It is interesting to note that the attempts at settlement generally came during periods of relatively favorable environmental conditions, which would have made this area a bit less forbidding than usual, as well as during times of increased regional population, when all the good land may well have been taken and some people were forced to seek out the more marginal areas.  The violence that appears to have accompanied the drought of the twelfth century, especially, suggests that when the good times came to an end social relations got very bad very fast.  Huckleberry and Billman suggest that the reason people did end up abandoning Cowboy Wash, the times when they were not attacked, was merely drought itself, which they were unable to cope with as well as other populations, even those who also used floodwater farming techniques, because the size of the watershed was relatively small and the amount of rainfall feeding the washes was also small, so the total amount of water they had to work with was much smaller even in good times than at place like Chaco with large watersheds.  In that context, even a small decrease in annual precipitation could be devastating, leading to failed harvests and the need to move away.

Non-Entrenched Escavada Wash from New Mexico Highway 57

Indeed, there is evidence that the time of the massacre at Cowboy Wash was very difficult for the people there.  Archaeobotanical studies of pollen and other plant remains showed that there was apparently little or no maize in or around 5MT10010 at the time of abandonment, which is quite surprising for a Pueblo site.  The plant remains that were there were mostly from wild plants such as chenopod, amaranth, and tansy mustard, all of which would have been available in the spring and likely would have been intensively collected if there were no stored corn available due to a failed harvest the previous fall.  In addition to pinpointing the season in which the incident occurred, this implies that times were very tough for the inhabitants of 5MT10010, and perhaps for their attackers too.  The coprolite showed no sign of having plant material in it, which suggests that whoever left it had not just eaten some corn at home before setting out to attack 5MT10010.

Another paper associated with the project, by Patricia Lambert, suggests another problem the Cowboy Wash inhabitants apparently had: disease.  In this paper Lambert reports on analyses of ribs of individuals at 5MT10010 and other sites in the Cowboy Wash area dating to various periods of occupation that had lesions on them suggestive of those seen in modern collections of individuals known to have died of tuberculosis and (to a lesser extent) other respiratory diseases.  These lesions were found in 11 of 32 individuals from Cowboy Wash that had enough of their ribs left to examine.  One of the individuals with lesions was from 5MT10010.  This was an adult woman who was not one of the victims of the attack at site abandonment but who had instead died earlier and been formally buried.  Lambert also examined comparative collections of remains from Pueblo Bonito at Chaco and Elden Pueblo near Flagstaff Arizona.  Only 3 of the 45 individuals from Pueblo Bonito and 2 of the 20 from Eldon Pueblo had similar lesions, suggesting that this disease was much more prevalent at Cowboy Wash than at these other sites, even though it was not absent at them.  Lambert notes that tuberculosis is an opportunistic disease that tends to strike people whose systems are compromised by other problems such as hunger and stress.  The evidence for physical violence in the Cowboy Wash sample, even setting aside the cannibalism assemblages, was much greater than in the other two samples as well.  Combined with the harsh environment, this suggests strongly that Cowboy Wash was a difficult place to live for several reasons.  Farming was possible but risky, and when conditions turned bad both hunger and violence from other hungry people were constant threats.

Given this context, the occurrence of extreme events such as cannibalism incidents at Cowboy Wash starts to make some sense.  Cowboy Wash is a place of extremes.
Huckleberry, G., & Billman, B. (1998). Floodwater Farming, Discontinuous Ephemeral Streams, and Puebloan Abandonment in Southwestern Colorado American Antiquity, 63 (4) DOI: 10.2307/2694110

Lambert, P. (2002). Rib lesions in a prehistoric Puebloan sample from southwestern Colorado American Journal of Physical Anthropology, 117 (4), 281-292 DOI: 10.1002/ajpa.10036

Read Full Post »

Looking East from the Pueblo Alto Trail

In my earlier post about Stephen Hall‘s recent paper reporting on maize pollen at Chaco Canyon dating as early as 2500 BC, I said briefly that this really shouldn’t be surprising to anyone who’s been following this kind of research closely, and also that I would discuss the context for it later.  Basically, the context is that there has been a considerable amount of evidence accumulating in the past twenty years or so firmly placing maize in the Southwest much earlier than most archaeologists had previously thought.  Much of this evidence has been gathered in a recent paper criticizing Jane Hill‘s arguments for the spread of maize having occurred as part of a migration of Uto-Aztecan speakers from Mesoamerica.  The earliest directly dated maize seems to be from the Los Pozos site in the Tucson Basin, with a date range of 2860 to 2470 BC (this represents the calibrated 95% confidence interval, as do all subsequent radiocarbon dates in this post unless noted otherwise).  According to the text of the paper, however, this date has been questioned, and the earliest uncontroversial direct date on maize comes from the aptly named Old Corn site near Zuni, with a range of 2460 to 2060 BC.  Note that the earliest date Hall found at Chaco (2567 to 2332 BC) has an upper bound slightly earlier than this, although the ranges overlap considerably.  Similarly early dates occur at some Tucson Basin sites and at Three Fir Shelter in northern Arizona, although the Three Fir Shelter date has a particularly large confidence interval.  The considerable geographic extent of these early maize dates implies that the initial introduction of maize to the Southwest may well have been quite a bit earlier than the earliest archaeological evidence for it.  It also suggests that at least in most areas, with some possible exceptions such as the Tucson Basin, maize was initially integrated into a hunter-gatherer lifestyle without causing major changes to either the subsistence system or the social structure of the groups adopting it.  This challenges many of the traditional assumptions about the effect of the introduction of agriculture on hunter-gatherer societies, including the idea that farming necessarily leads to an immediate shift to settled village life.  There is little to no evidence in most areas of any such shift for thousands of years after the earliest evidence for maize agriculture, suggesting that the impetus for such a transition (which did indeed happen in almost all parts of the Southwest eventually) must be sought elsewhere.

Una Vida from Petroglyph Area

Okay, so there’s plenty of evidence for agriculture as early as the pollen dates at Chaco in many parts of the Southwest, but Chaco ain’t Tucson.  The high, dry, harsh environment of the central San Juan Basin seems particularly unsuitable for agriculture compared to a lot of the other areas with early evidence for maize.  So surely this is a surprising finding at least for the local area, right?

Actually, no.  Evidence for the early use of maize in the general area of Chaco, though until now not within the canyon itself, has actually been out there for over twenty years, although it doesn’t seem to have gotten much attention in the subsequent literature.  It is described by Alan Simmons in an article from 1986, reporting on research done initially as a cultural resources management (CRM) project in connection with plans for coal mining in the area directly to the east of Chaco.  This project, known as ADAPT I, found many typical Archaic sites in the area, some of which were excavated as mitigation activities because of the expected impacts of mining.  (I believe this mining operation never actually happened, but I don’t know any of the details.)  These Archaic sites were typical for the San Juan Basin, which is to say that they were mostly lithic scatters with few diagnostic artifacts or datable materials, but a few of them ended up being very surprising in having more under the surface than was apparent at first, including possible hearths or ovens, some of which contained maize pollen associated with charcoal that was radiocarbon dated to the Archaic period and one of which even contained maize macrofossils that were directly dated to the late Archaic.  (The dates Simmons relates are apparently uncalibrated and are therefore not directly comparable to the calibrated date ranges given above, but they are comparable to the uncalibrated dates given by Hall for the pollen samples, including at the early end.)

Looking North from New Alto

This very unexpected result led to a new project, known as the Chaco Shelters Project, to try to get more data on the Archaic period in the Chaco area through intensive study of the type of site most likely to contain well-preserved material: rockshelters.  Two shelters were excavated, both outside of the park boundaries, one to the east (Sheep Camp Shelter) and one to the west (Ashislepah Shelter).  Neither provided much in the way of artifacts, which was something of a disappointment, but both showed evidence of Archaic use, and Sheep Camp Shelter contained macrobotanical remains of both maize and squash.  Neither contained maize (or squash) pollen.  Both maize and squash remains were directly dated to the late Archaic.  The squash results were more important, as the resulting dates were at the time the earliest evidence for the presence of squash in the Southwest.  Despite the presence of these direct dates, the earliest dates Simmons had were on charcoal associated with the maize pollen at the ADAPT I sites, and these could potentially be questioned given the known problems with this kind of indirect dating.  Now that Hall has come up with direct dates on the pollen itself which cover roughly the same timespan, however, Simmons’s indirect evidence looks more convincing than it may have at the time.

At the time Simmons was writing, there was much less direct evidence of Archaic agriculture in the Southwest than there is now, and the few reported early dates were problematic and disputed.  He therefore has a substantial and quite useful discussion of the general issue in addition to reporting his specific data.  He clearly comes down on the side advocating a gradual shift from hunting and gathering to agriculture, with maize being initially adopted by hunter-gatherers as part of a preexisting subsistence system and only becoming the primary means of subsistence considerably later.  This view was generally associated with arguments for in situ development of Anasazi culture out of the local Archaic tradition, and was opposed by those who preferred to see agriculture as being introduced later and all at once, perhaps as part of a migration of agriculturalists from the south (a position now maintained by Jane Hill, among some others).  With regard to the Chaco area specifically, Simmons accounts for the differences between the open ADAPT I sites (with maize pollen but little macrobotanical evidence) and Sheep Camp Shelter (maize and squash macrofossils but no pollen) by proposing that maize was initially integrated into a subsistence system involving seasonal mobility, with spring and summer being spent in the ADAPT I area, where the many sand dunes would have fostered the growth of wild plants, and winter being spent in the more protected rockshelters in the canyons to the west.  When maize and squash were added to the seasonal round, they would have been planted on or near the dunes in the spring, harvested in the fall, and taken back to the shelters to provide durable, storable food for the harsh and largely barren winter.  He admits that the shelter evidence, especially, is a bit weak, as it doesn’t really support the idea of extensive winter use of the shelters, but there were apparently many Archaic sites near the shelters that may provide more support for occupation of the general area during the winter.  He therefore concludes that the model he proposes is generally consistent with the data although more research is needed to confirm it.  He mentions Atlatl Cave, in the park and excavated by the Chaco Project, as one possible additional data point in favor of his model.

Pueblo Bonito from Peñasco Blanco

Hall’s new pollen data from within the canyon provides some support for Simmons’s model, especially in backing up the indirect dates with direct ones, but it also suggests some possible modifications to it.  It clearly seems to indicate that the canyon itself as well as the dunes to the east was used to grow corn during the Archaic.  This casts some doubt on Simmons’s proposal of seasonal mobility, at least in the way he frames it.  Growing corn in the canyon would imply occupation of it, perhaps in rockshelters such as Atlatl Cave, during the spring and summer in addition to (or instead of?) during the winter.  That is, Simmons’s seasonal mobility model could perhaps be “condensed” into a similar model of subsistence activities throughout the year, but with year-round residential occupation in the canyon.  People would presumably have still traveled around to gather resources in different areas at different times of year, but this would be “logistical” as opposed to “residential” mobility, with hunting and gathering parties setting out from a more permanent base camp solely to collect resources as opposed to moving the whole group to the location of the resources.  It is of course also possible that Simmons’s model should be modified in some other way, keeping the seasonal mobility but changing the role of the canyon in it, but it’s hard to see where else in the area would have been more suitable for winter occupation.

One of Simmons’s suggestions, that the advent of corn agriculture may have made the Chaco area an easier place to live by providing a fairly reliable food source in a place with limited and unreliable wild food resources, is particularly interesting.  The San Juan Basin is well-known for its considerable Archaic population, which has generally been interpreted as indicating seasonal mobility and specialized adaptations to the region’s sparse resources, but what if that population was actually supported in part by incipient maize (and squash) agriculture?  People often marvel at the apparent barrenness of the Chaco environment and the oddity of the idea that anyone would try to farm there, but this is another way to look at the harshness of the environment.  To put it differently, farming in Chaco is certainly difficult and risky, but can you imagine trying to live there without farming?
Merrill, W., Hard, R., Mabry, J., Fritz, G., Adams, K., Roney, J., & MacWilliams, A. (2009). The diffusion of maize to the southwestern United States and its impact Proceedings of the National Academy of Sciences, 106 (50), 21019-21026 DOI: 10.1073/pnas.0906075106

Simmons, A. (1986). New Evidence for the Early Use of Cultigens in the American Southwest American Antiquity, 51 (1) DOI: 10.2307/280395

Read Full Post »

Petroglyph Panel above Crevice Containing Packrat Midden CC-3

One important line of evidence in understanding the climatic history of Chaco Canyon, a subject of considerable interest given the harsh aridity of the current climate and the incongruous grandeur of the archaeological remains, has been the study of packrat middens.  These are collections made by packrats of materials found near their nesting locations, which they collect and then seal with urine.  The key thing about these middens, in addition to the preservation ensured by the protective coating of urine, is that the packrats have fairly small territories within which they collect material, so the contents of the middens, which can easily last for thousands of years, reflect the vegetation of the immediately surrounding area at the time the midden was created.  Since they generally consist of organic material that can be radiocarbon dated, the middens can potentially offer enormous insight into climate change over time.

There is some difficulty with this, however, because the proper interpretation of the contents of the middens is not always clear.  Interpretations are often based on the visible plant remains (known as “macrofossils”), but these may be biased by behavioral factors owing to the diet and habits of the packrats themselves.  Juniper, for example, tends to be overrepresented because it is one of the main components of the packrat diet.  One way to avoid this problem is to look not just at the macrofossils but also at the pollen grains contained in the middens.  Since these are too small for the packrats to be consciously choosing them, they would have to be deposited by wind or other natural processes, which may make them more reliable clues to the relative abundance of various plant species as opposed to the mere presence or absence of species.

Crevice Containing Packrat Midden CC-3

One researcher who has long been associated with this point of view is Steve Hall, who was for many years a professor of geography at the University of Texas.  He is now retired and has a consulting firm in Santa Fe specializing in the geology of Southwestern archaeological sites.  He has been involved with packrat midden studies at Chaco since the 1980s, and has recently published an important article reporting on a recent reanalysis of some of the middens that resulted in some remarkable conclusions.

What Hall found in looking at the midden samples was corn pollen.  This is not surprising in and of itself, since the Chacoans were of course an agricultural people with a corn-based subsistence strategy.  The focus of the paper, however, is on radiocarbon dating of the pollen grains, which resulted in some remarkable findings.  Conventional radiocarbon dating requires much larger samples than would be possible for pollen grains, but the relatively new accelerator mass spectrometry (AMS) technique requires only very small samples, and also tends to give more precise dates than traditional radiocarbon dating.  Hall dated pollen samples from two packrat middens in crevices near Casa Chiquita, referred to as CC-2 and CC-3.  These are both right along what is now the “Petroglyph Trail” section of the Peñasco Blanco trail, and fragments of the middens can be seen from the trail, although they are now substantially broken up from sampling for study.  CC-3 is right beneath one of the best-known petroglyph panels on the trail.  CC-2 is not as directly associated with any particular petroglyph panel, but it is in close proximity to a few.

Crevice Containing Packrat Midden CC-2

The results basically showed that the corn pollen was old.  Some of the samples were very old indeed, on a par with the oldest known maize in the Southwest.  The oldest sample, from CC-3, had a 95% probability of being from between 2567 and 2332 BC.  Another sample, from CC-2, had a 95% confidence interval of 1457 to 1254 BC, while the rest of the samples from both middens were later but still pretty old, dating to the 800s through 400s BC.  In addition to the AMS dating, Hall measured the abundance of maize pollen in the overall pollen samples from the middens and looked at the size of the pollen grains themselves.  He found that maize pollen was quite abundant, and that the grains were consistently bigger than comparison samples of modern and later Chacoan maize pollen.  Since maize pollen is pretty heavy in general, and this particular maize pollen was even heavier than usual, he concluded that it couldn’t have traveled far, and that it must have been blown into the crevices from a cornfield directly in front of them, where the packrats later incorporated it into their middens along with various other materials.  One thing he points out in the article is that twigs from the same middens dated to much later than the pollen, which casts doubt on the common practice of dating middens only by single macrofossils.  It seems that material incorporated into the middens can vary considerably in age, and direct AMS dating of pollen is a better approach to determining its age than dating of associated macrofossils.  There’s a bit more to the article, but those are the highlights.

Proposed Site of Archaic Cornfield near Casa Chiquita

This actually shouldn’t be all that surprising to anyone who has been following recent developments in the archaeology of the Archaic period in the Southwest, but I have not been, and I found it pretty surprising.  After reading this paper I looked into earlier research a bit and found that there has been quite a bit of direct dating of maize and associated materials resulting in comparable dates, including some from rockshelters near Chaco.  I knew that there was considerable evidence for early maize further south, in places like the Tucson area, but it seems that evidence for Archaic corn agriculture is pretty well established further north as well.  The implications of this for Southwestern archaeology in general are therefore fairly limited, and it mostly just adds another data point to the accumulating evidence on Archaic agriculture.

The implications for Chaco specifically, however, are huge.  This shows pretty convincingly that agriculture in the canyon goes back to long before the main flourishing of the Chaco System in the eleventh and early twelfth centuries AD, and it suggests that Chaco’s importance may go back to thousands of years before that at least on some level.  One interesting thing Hall points out is the proximity of these middens, and by implication the nearby cornfield, to Atlatl Cave, a well-known Archaic site on the mesa top about a kilometer away.  The radiocarbon dates for Atlatl Cave match up pretty closely with the later dates on the corn pollen, and Hall suggests that the people who lived there were the same ones growing the corn in the canyon below.  It’s a reasonable suggestion, and it puts a lot of interpretations of the early prehistory of Chaco in a new light.  I’ll be reading up on the Archaic period and trying to understand what this discovery means for our understanding of Chaco during that time.  I should have some more posts on the topic soon.  For now, though, I’ll just note that this may indicate more continuity of occupation or at least cultural knowledge of Chaco than is generally assumed.
Hall, Stephen A. (2010). Early maize pollen from Chaco Canyon, New Mexico, USA Palynology, 34 (1), 125-137 : 10.1080/01916121003675746

Read Full Post »