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Hohokam Astronomy

Phoenix, Arizona

Phoenix, Arizona

Today is the summer solstice, so I figured I would take a break from my (slowly) ongoing series of posts on the Pueblo I period in the northern Southwest to take a look at evidence for ancient astronomical knowledge in a different part of the Southwest. This is in part an outgrowth of my recent thoughts on the role of astronomy in the rise of Chaco Canyon to regional prominence, which in turn was spurred in part by the realization that Chaco appears to show the earliest evidence for complex astronomical knowledge in the northern Southwest. The idea, which I explored exactly one year ago in this post, is that by the eleventh century AD the Chacoans developed a knowledge of astronomy that they were able to use as esoteric ritual knowledge to enhance the canyon’s role as a political and economic power throughout the region.

This idea led me to wonder, however, about the history of astronomical knowledge in the southern Southwest, which was culturally quite different from the northern areas influence by Chaco. In particular, the Hohokam of the southern Arizona deserts show both a longer history of intensive agriculture and a closer connection to Mesoamerican societies further south, both attributes that could be relevant to their knowledge and use of astronomy. If evidence for that knowledge among the Hohokam long predates that evidence at Chaco, this leads to interesting questions about the origins of Chacoan astronomy. If it doesn’t, that leads to other interesting questions about both societies.

Luckily, the same special issue of the journal Archaeoastronomy that contains an article on Chacoan astronomy that I discussed in a previous post also contains one on Hohokam astronomy. This article, written by Todd Bostwick, discusses evidence for astronomical alignments in Hohokam monumental architecture and rock art, as well as the astronomical and calendrical practices of the modern O’odham people who inhabit the same area (and whose relationship to the Hohokam is unclear and controversial, although Bostwick doesn’t discuss this). Bostwick’s focus is on the Phoenix area, which is considered the Hohokam heartland.

Bostwick documents a wide range of possible alignments in Hohokam architecture and petroglyphs, primarily solstice-oriented. These include a large number of rock-art sites in and around the mountains that show clear alignments to the solstice sunrises, particularly associated with a distinctive dot-in-circle motif that may be a sun symbol. There are also some rock art sites with complex patterns of light and shadow interacting with the petroglyphs on the solstices, similar to the famous “Sun Dagger” petroglyph on Fajada Butte at Chaco. In architecture, perhaps the most intriguing alignments are a series of holes in the upper walls of the “Big House” at Casa Grande Ruins National Monument which show possible alignments primarily to the equinox sunrise, and perhaps to some of the lunar standstill moonsets as well. There are also astronomical alignments associated with platform mounds at the villages of Mesa Grande and Pueblo Grande.

The rock art alignments are notoriously difficult to date, of course, and the aforementioned architectural features all date to relatively late in the Hohokam sequence and are therefore not very useful to understanding the origins of Hohokam astronomical knowledge. There are, however, features at the earlier village of Snaketown that may have had an astronomical purpose, although it is less straightforward than the others.

Snaketown was the preeminent village of the Hohokam during the Sedentary period, which is roughly contemporaneous with the florescence of Chaco (ca. AD 900 to 1150), although its history extends back several hundred years earlier. It was not occupied into the following Classic Period, when the other villages mentioned above reached their peaks. There is an alignment between the central plaza of Snaketown and Gila Butte, a geological formation to the southeast that is considered sacred by the O’odham. On the winter solstice, the sun rises between the two peaks of the butte when viewed from the plaza, and Bostwick suggests that the siting of Snaketown may be related to this alignment. If so, this would imply knowledge at least of solstice alignments was much earlier in the Hohokam area than further north, but without clear evidence from earlier periods this must remain speculative.

Another intriguing but ambiguous feature at Snaketown is the platform mound known as Mound 16, at the northeast edge of the plaza. This circular mound is surrounded by a series of 52 postholes, placed fairly regularly but with gaps on the northeastern, southern, and southwestern sides of the mound. There are no structures or postholes on top of the mound, but there is one hearth at the southern end associated with one of the gaps in the ring of postholes. This clearly seems to indicate some sort of ceremonial or symbolic use for the mound, although it’s not clear what that would have been. Bostwick notes that some of the posts seem to align with the solstice and equinox sunrise positions as viewed from atop the mound, and he suggests that Mound 16 may have served as a “ritual sundial” of some sort. In this respect it is very reminiscent of the “Woodhenge” ring of posts next to Monk’s Mound at Cahokia, which has also been interpreted as an astronomical marker. Still, this interpretation is rather speculative at this point and Bostwick concludes his discussion of the mound with a call for further research on its possible astronomical alignments.

Reconstructed "Woodhenge" at Cahokia

Reconstructed “Woodhenge” at Cahokia

The upshot of all this from my perspective is that the history of astronomical knowledge in the southern Southwest actually seems to be just as murky as that further north. In both cases the most apparent astronomical alignments in architecture seem to date quite late, although this doesn’t say much about the time depth of the knowledge behind them. There are a few intriguing hints in more general aspects of Hohokam society that may provide some insight, however.

One is the adoption here of the Mesoamerican ballgame, played in distinctive courts that are primarily associated with the Sedentary period and the florescence of Snaketown (which has two). As Bostwick notes, in Mesoamerica the ballgame was often associated with astronomical symbolism and particularly with the sun and the calendar. Its introduction among the Hohokam around the beginning of the Sedentary period may therefore indicate the introduction of certain religious motifs or practices from the south that emphasized celestial, and especially solar, patterns.

Bostwick also notes one admittedly speculative but very interesting theory regarding this introduction which associates it with a solar eclipse in AD 797 which would have been visible to the Hohokam, and which was followed a few years later by a series of disastrous floods. It’s possible that the Hohokam perceived the eclipse as an omen predicting the floods, and that they adopted new religious practices associated with the sky to prevent further disasters like this. Another eclipse in AD 1076 may have been associated with the abandonment of Snaketown and other major Sedentary period villages and the reorganization of Hohokam society into a new form during the Classic period. Notably, this change included the decline of the ballcourt system and the rise of new forms of ritual associated with platform mounds. A subsequent solar eclipse in AD 1379 was again followed a few years later by catastrophic floods that many scholars consider important factors in the ultimate collapse of Hohokam society.

This eclipse theory is fascinating, although it’s obviously very speculative and probably impossible to prove or disprove conclusively. There was a lot of other stuff going on at the same time as each of these societal transformations, of course, and it’s likely there were multiple factors involved in each case.

It’s still not clear what role Hohokam astronomical knowledge might have played in the development of similar knowledge at Chaco. The Chacoans may have noticed alignments in their local environment basically independently of anything similar going on further south, they might have heard rumors about Hohokam astronomy that spurred them to develop their own, or they might have had detailed knowledge of Hohokam practices that they used to implement similar practices themselves. The extent to which the Chacoans and Hohokam were aware of each other and the extent to which they interacted either directly or indirectly are important questions for understanding Southwestern prehistory, and they have not received very much attention from scholars who specialize in either society (although some of Steve Lekson’s recent work has been an important exception). The murky history of astronomical knowledge in both areas doesn’t seem to shed much light on these questions at this point, but with further research it may become more illuminating. Happy solstice.
ResearchBlogging.org
Bostwick TW (2010). Exploring the Frontiers of Hohokam Astronomy: Tracking Seasons and Orienting Ritual Space in the Sonoran Desert Archaeoastronomy, 23, 166-189

Animas River, Durango, Colorado

Animas River, Durango, Colorado

The fourth chapter of Crucible of Pueblos discusses the eastern portion of the Mesa Verde region, essentially the northern portion of the watershed of the San Juan River from the La Plata drainage east to the San Juan headwaters. This area has seen less research than some other parts of the Southwest, but several major salvage projects in recent decades have added a lot of data on Pueblo I period settlement in particular. The most important of these has been the Animas-La Plata Project associated with the inundation of Ridges Basin to create Lake Nighthorse south of Durango. These projects haven’t revolutionized our understanding of the Pueblo I period the way the Dolores Project did in the Central Mesa Verde region in the 1980s, but they have added large bodies of systematically collected data to broaden our understanding of the period.

The picture that emerges from this evidence shows the Pueblo I period to have been a dynamic, complex time in this region. Indeed, in some respects “chaotic” might be an appropriate descriptor. Population movement, both within the region and between it and other regions nearby, was frequent, sites were short-lived, and evidence for violence is abundant. The population fluctuated wildly but was never very large compared to other areas, but even this small population seems to have been culturally and perhaps ethnically diverse, which may have contributed to the instability and violence. Some of the earliest aggregated villages in the northern Southwest arose in this region during the eighth century AD, but they all appear to have been highly unstable: none lasted more than a few decades, and most appear to have met violent ends. Perhaps relatedly, these villages never held more than a small portion of the overall regional population, in contrast to early villages in some other regions. By the end of the Pueblo I period around AD 900 most parts of the region were largely depopulated, with the residents apparently moving primarily to the south, where many of them likely ended up at Chaco Canyon and were involved in the rise of the Chaco Phenomenon over the course of the tenth and early eleventh centuries.

The authors of this chapter divide their region into four “districts”: La Plata, Durango, Piedra, and Navajo Reservoir/Fruitland. While showing similarities in material culture suggesting connections with each other, the districts have markedly different demographic trajectories, and it seems clear that there was significant population movement among them over the course of the Pueblo I period.

Despite an earlier Basketmaker II occupation, Basketmaker III period settlement was limited to nonexistent in most of the districts, implying that the Pueblo I occupation was primarily the result of migration into the region. Only the La Plata district shows clear evidence for a small BMIII occupation, and even this is probably too small to account on its own for the larger population in the district during Pueblo I. It appears, then, that beginning in the AD 720s there was a migration of people into the La Plata and Durango districts, probably from the south. Site densities increased markedly around 750, especially around Durango, suggesting a further wave of migration, again from the south. It was at this time that the earliest villages began to develop in these areas, although most of the population continued to live in widely scattered hamlets and individual residences. These villages were short-lived and seem to have collapsed in the early 800s, in some cases with evidence for intense violence including, at Sacred Ridge in Ridges Basin, the earliest evidence for the sort of “extreme processing” (probably including cannibalism) of human remains that would recur periodically in later periods of Pueblo prehistory.

The collapse of the early villages in the Durango district appears to have coincided with a general depopulation of that district, with residents emigrating in multiple directions. Some went west and appear to have contributed to the rise of large villages in the Central Mesa Verde region, particularly in the Dolores area, where one large and well-documented community, Grass Mesa Village, shows evidence in its material culture for strong ties to the east. Other Durango people may have gone south into the Frances Mesa area in the lower Animas River valley, possibly mixing with other groups migrating north at the same time. This occupation was short-lived and may have ended with the people moving north into the Dolores area to join the villages there. Some Durango people may also have gone east to form the first Pueblo I occupation in the Piedra district, although this area has seen less research than others and the picture isn’t as clear. Recent surveys do suggest that the Piedra was somewhat marginal to developments elsewhere in the region during Pueblo I, and that its population was both smaller than had been thought and mostly limited to the late Pueblo I period. The fate of the La Plata population is less clear, but there is a definite decline in site numbers after AD 800 coinciding with an increased number of sites in the Mancos River drainage to the west, suggesting emigration to the west there as well.

Chimney Rock Great House

Chimney Rock Great House

As it turned out, the Dolores villages weren’t very stable either, and after their collapse in the mid- to late ninth century people seem to have migrated back into the eastern Mesa Verde region. A surge of immigration into the Fruitland/Navajo Reservoir district after about 880 contributed to the highest regional population of the whole Pueblo I period, although it still wasn’t very high (3,000 people at most regionwide, and likely more like 2,000). The Piedra district also saw a considerable increase in population at this time. The Fruitland/Navajo Reservoir occupation was short-lived, with more evidence of violent ends for some village sites, and it seems that most or all of the people moved south, with at least some of them joining the growing communities in and around Chaco Canyon. There may have been some migration south from the Piedra district as well, but it continued to be occupied into the Pueblo II period after 900. The Piedra people seem to have been somewhat isolated from developments elsewhere in the Pueblo world during early Pueblo II, which is unsurprising given that they were left quite isolated geographically by the depopulation of the Animas drainage and Navajo Reservoir area. They don’t seem to have been completely cut off, however, and ongoing contact with Chaco in particular is suggested by the development of the Chimney Rock great house with its remarkable astronomical alignments in the eleventh century.

There are several noteworthy characteristics of this pattern of settlement and migration, which the authors of this chapter point out. One is the obvious importance of population movement, versus natural increase or decrease, in explaining the wild demographic swings both in the region as a whole and among its individual districts during this period. It was a very dynamic period, when people rarely lived in the same place for more than two or three generations. It’s not clear entirely why, but one reason is likely linked to one of the other noteworthy characteristics: widespread violence, including some of the most extreme violent incidents in the whole archaeological record of the Southwest. Interestingly, much of this violence, including the “extreme processing” incident at Sacred Ridge, appears to have been linked to internal conflicts within communities, especially the early villages. This may in turn explain why relatively few people in this region lived in villages, although it still leaves open the question of why anyone did. The authors suggest that one factor may have been the perception of safety in numbers in a chaotic era, although this ultimately proved to be illusory. It’s not clear to what extent warfare between communities was actually occurring, however, and the widespread popularity of a scattered settlement pattern suggests it may not have been that major a concern for most people. On the other hand, palisades around individual residents units are fairly common in the region, so it may be primarily a matter of different strategies for dealing with violence.

One other noteworthy thing about the violence is that the “extreme processing” phenomenon appears to have been exclusive to the eastern Mesa Verde region during this period. This is interesting because in later periods it occurs in other regions, most notably in the Central Mesa Verde region during the mid-twelfth century, where it is possibly associated with the collapse of the Chaco system. There has been much dispute and discussion about the occurrence of cannibalism as part of at least some of these assemblages, which I’ve discussed at length before. The fact that it appears earliest in the eastern Mesa Verde region during Pueblo I, when it appears to be limited to that region, adds an important piece of context for understanding the phenomenon. While the occurrence of ritual cannibalism in Mesoamerica has led some to look there for the roots of cannibalism in the Southwest, there are some important differences in the apparent practices behind the assemblages that make a Mesoamerican source difficult to document, and if the eastern Mesa Verde region was in fact the part of the Southwest where these practices originated that makes the Mesoamerican connection even more tenuous. While the exact connections between specific Basketmaker and Pueblo populations in different areas are hard to pin down, it’s generally thought that the eastern Basketmakers were both ancestral to later Pueblo populations in the same areas and descended from earlier Archaic populations. Importantly, these eastern groups generally show much less evidence for Mesoamerican influence than western groups, among whom “extreme processing” events are both much rarer and, when they do occur, much later than in the east. Obviously it’s not that there was no Mesoamerican influence among eastern groups, since they did have maize agriculture and so forth, but there’s much less evidence for specific, direct influence than in the west. This implies that “extreme processing,” including cannibalism, may actually have been a practice that developed indigenously in the eastern Mesa Verde region and spread to other parts of the northern Southwest as part of the widespread population movements following Pueblo I.

Finally, the violent and chaotic nature of the Pueblo I period in the eastern Mesa Verde region, whatever the underlying reasons for it, adds some context for the attractiveness of new social formations in other regions, such as the Pueblo I villages in the Dolores area and the emerging great-house communities of early Pueblo II in and around Chaco. While the Dolores villages were not ultimately able to deliver the kind of peace and stability that immigrants from the eastern Mesa Verde region may have been looking for, Chaco apparently was. Furthermore, once Chaco rose to regional prominence in the eleventh century it was able to extend that peace and stability over an unprecedentedly large area of the northern Southwest, including the eastern Mesa Verde region itself. Understanding how the system that emerged in Chaco Canyon was able to achieve this remarkable feat when no one had succeeded at anything like it before is one of the most important questions in Southwestern prehistory, and it is still very much an unanswered one. One important piece of the puzzle, however, is clearly the Pueblo I context in the Chaco area itself, and it is to this that we now turn.

Chaco Street in Aztec, New Mexico

Chaco Street in Aztec, New Mexico

Utah Welcome Sign

Utah Welcome Sign

The third chapter of Crucible of Pueblos deals with the western part of the Mesa Verde or Northern San Juan region, which basically corresponds to what is now the southeastern corner of Utah. In this context the area is bounded by Cedar Mesa on the west and the Abajo Mountains on the north, as well as by the borders with Colorado and Arizona on the east and south. This is a fairly standard way to define this area archaeologically except that the western boundary is more restrictive than usual, which appears to mainly be a decision based on the near-total lack of sites dated to the Pueblo I period west of the eastern edge of Cedar Mesa. (There are actually Pueblo sites dating to this period much further west in southwestern Utah and southern Nevada, the so-called “Virgin Anasazi,” but they aren’t included in this book at all for some reason.)

The authors divide their study area into a series of physiographic sub-regions based primarily on elevation, which is a useful way to track changes in occupation patterns over the course of the period they discuss. It’s also a different approach to defining sub-regions than most of the other chapters in the book use. These sub-regions are important because the differences in precipitation and growing season length among them seem to have been important factors behind shifting settlement patterns during the period of interest. These shifts seem to have mainly taken place across the region rather than separately in spatial sub-regions such as drainages, as was the case in some other regions.

One way this region differs from others, and especially from the Central and Eastern Mesa Verde regions, is that there has been a relative lack of large-scale salvage excavation projects to provide large amounts of detailed archaeological data. Instead, most data is from surveys and small-scale excavations, and detailed chronological information in particular is missing for most sites that have been recorded. Rough dating of sites to Pecos Classification period at best based on frequencies of a few ceramic types is the norm here, which limits the comparability of data on trends in settlement over time. Nevertheless, the authors of this chapter do their best to come up with a coherent narrative of settlement during the Basketmaker III and Pueblo I periods in this area, which seems to have been an important one for understanding the cultural development of early farming populations and the origins of aggregated villages.

The most striking pattern in the population dynamics of this region in the Basketmaker III and Pueblo I periods is of apparent cycles of population growth and decline on the scale of decades and of greater magnitude than can be explain by internal demographic processes, implying migration into and out of the region multiple times. Most interestingly, these cycles appear to be largely complementary to similar cycles in other nearby regions, especially the Central Mesa Verde region just to the east. This strongly implies that one of the major factors in population changes in both these regions was movement between them.

To go into greater detail, the story told in this chapter begins in the seventh century AD with the expansion of Basketmaker III populations across the region from the narrow area of Basketmaker II settlement along the San Juan River and its major tributaries. The authors attribute this expansion in part to the introduction of beans and pottery, which freed farming populations from dependence on outcrops of limestone to cook with their corn for nitrogen-fixing purposes. Population spread especially into the upland areas with deep soils well-suited to dry farming. Over the course of the Basketmaker III period scattered hamlets began to consolidate into “proto-villages” with public architecture such as oversized pit structures surrounded by scattered households. The authors note the similarity of this pattern to the later Pueblo II great house communities, which is indeed an interesting parallel.

There appears to have been a regional population decline in the early eighth century, although this may be an artifact of the limited data set and difficulty assigning sites to precise time periods. In any case, there is evidence of a noticeable population increase after AD 750, with several villages of tightly clustered households containing public architecture appearing, along with a considerable number of smaller residential sites and a few sites in highly defensive locations, especially at the western edge of the region near Cedar Mesa. The population increase was accompanied by the introduction of a strikingly different type of pottery, Abajo Red-on-orange, which shows many similarities to pottery from the Mogollon region far to the south and likely reflects long-distance migration of some sort. There were still many continuities in architecture and other aspects of material culture, however, which suggests that these migrants combined with local populations rather than replacing them.

The largest and most famous of the villages that developed during this early Pueblo I period is Alkali Ridge Site 13, excavated by J. O. Brew in the 1940s. This site consisted of a series of long, continuous arcing roomblocks, made up of “room suites” of one “habitation” room backed by two smaller “storage” rooms. This is a pattern that would become standard for Pueblo I villages at a slightly later date, and would endure in various forms for centuries. Site 13 consists of six of these arcs, four of which were excavated by Brew. Three of the arcs excavated by Brew also had oversized pit structures with highly formalized features suggesting possible use as public architecture of some sort.

There were other village-sized sites that were established at this time, although few have been excavated. These are among the earliest sites of this size and level of organization in the northern Southwest, and continuities with later sites in other regions suggest they may have been very influential on later developments.

In addition to the early village sites, defensive sites on high, inaccessible promontories began to appear during the early Pueblo I period. These sites have not been studied in any depth, and little is known about them. Some appear to have evidence of extensive residential populations and/or public architecture, while others don’t. One intriguing pattern is an apparent line of them at the western edge of the region along the eastern margins of Cedar Mesa. This, combined with the lack of Pueblo sites to the west, has suggested to some researchers that there was a buffer area or “no-man’s-land” between the Pueblo population in southeastern Utah and early Fremont populations northwest of the Colorado River during this period. It’s worth noting, however, that there were also a few of these apparent defensive sites well within the Mesa Verdean Pueblo region, including the Fortified Spur site near the Colorado-Utah border, so tensions may have been internal as well as external at this point.

During the middle Pueblo I period from AD 825 to 880 there appears to have been a regional population decline, although again this may be due in part to data gaps. It is noteworthy, however, that this is the period of a major population increase in the Central Mesa Verde region to the east, including the formation of the well-known cluster of aggregated villages in the Dolores River Valley, some of which show some striking similarities to earlier Utah villages such as Site 13. It is reasonable to postulate that a pattern of emigration from southeast Utah into southwest Colorado led to this pattern. Southeast Utah wasn’t completely depopulated, however. In addition to scattered small sites throughout the region, there are a very few larger communities firmly dated to this period, including an intriguing site on Elk Ridge called the Pillars that has extensive evidence for middle Pueblo I residential architecture and some tentative evidence for public architecture as well. There are several other sites in the same general area that have more tentative evidence for occupation during this time, and it seems this may have been one of a handful of population clusters in the region during a time of otherwise low population.

After AD 880 population rapidly increased again, and many large villages were built between this point and AD 950. This was a period of rapid depopulation in the Central Mesa Verde region, again suggesting a complementary pattern of migration between the two regions. Many of these new village sites were in highly defensive locations, including some that were nowhere near the frontiers of the region. There is also an intriguing pattern of continuity in location between these early villages and later Pueblo II great house communities from the eleventh century. This pattern is made even more intriguing by two phenomena:

  1. Some of these sites, such as Red Knobs and Nancy Patterson Village, have evidence for masonry roomblocks similar to the “proto-great houses” known from many sites in New Mexico in and around Chaco Canyon during this same time.
  2. There seems to have been another depopulation of southeastern Utah around AD 950, implying that population at these sites was not actually continuous despite these similarities.

It has long seemed to me that southeastern Utah is a crucial area for understanding Chaco. There are several lines of evidence suggesting that at least some people living in Chaco Canyon and involved in its rise to regional dominance had strong ties to Utah, and I suspect those ties were more important in the emergence of the Chaco system than has been generally recognized. This chapter adds some much-needed context on the earlier history of Pueblo populations in Utah, and to me it strongly reinforces those ideas about the importance of Utah to Chaco. The exact nature of these relationships and their importance is still unclear, and the relatively sketchy data available make it harder to figure out, but it still definitely seems like there is something important here.

McPhee Reservoir and Mesa Verde Escarpment from McPhee Campground

McPhee Reservoir and Mesa Verde Escarpment

The second chapter of Crucible of Pueblos discusses the Central Mesa Verde region, which is defined as basically the southwestern corner of Colorado, bounded on the west and south by the modern borders with Utah and New Mexico, on the east by the La Plata River valley, and on the north by the highlands north of the Dolores River. This is the region where Pueblo I period villages have been most extensively studied, primarily by the Dolores Project during the construction of McPhee Reservoir in the 1980s and in subsequent research by archaeologists building on that work. As a result, there’s not a whole lot that’s new in this chapter for someone who has been following the literature on this topic, although it does make a good introduction to the subject for someone who hasn’t. It also discusses some parts of the area, especially the northern and eastern fringes, that have seen much less research than the well-studied Great Sage Plain (including the Dolores sites) and Mesa Verde proper. Overall, the data assembled here is among the most detailed and reliable available to analyze demographic trends and population movements during the Pueblo I period in the northern Southwest.

Among the key factors that the authors discuss are the inherent attractiveness of this region to early farmers because of its good soil and relatively favorable climatic conditions compared to other nearby areas. Indeed, this is the only part of the northern Southwest that has seen extensive dry farming in modern times, and it is still primarily agricultural in use. This makes it unsurprising that early farmers would have concentrated here, as indeed they did, starting in the Basketmaker III period ca. AD 600 and increasing steadily in population through about 725. These early sites generally consisted of scattered hamlets presumably housing individual families. Villages, which in this context means clusters of multiple residential roomblocks in close proximity, began to appear around 750, often in association with great kivas, which had previously been rare in this region for reasons that are unclear.

Villages to both the west and east, discussed in subsequent chapters, date to the same period as these early ones in the Central Mesa Verde villages, and there was a striking variety in community organization and layout across the broader region. The dissolution of the eastern and western villages seems to have contributed to an influx of population into the Central Mesa Verde area in the early ninth century, resulting in the largest and densest concentration of population seen to that date. Village layout also became more standardized, with two main patterns dominating, one associated with great kivas and another including U-shaped roomblocks that were likely ancestral to later “great houses.” These villages, most extensively documented at Dolores, were however short-lived, and by the early tenth century the area was almost completely depopulated, with the former inhabitants apparently moving primarily to the south, into the southern part of the San Juan Basin, where they seem to have played a key role in the developments that led to the rise of Chaco Canyon as a major regional center in the eleventh century.

As I said before, none of this is groundbreaking information at this point, and I’ve discussed some of the implications of the Dolores data before. It is however useful to have a synthesis of this region during this important period to refer to, and this chapter works well for that purpose.

Foreshadow: Introduction

McPhee Reservoir, Dolores, Colorado

McPhee Reservoir, Dolores, Colorado

A few years ago I did a series of posts called “Aftermath” that consisted of short commentaries on the chapters in The Prehistoric Pueblo World, a volume edited by Michael Adler that synthesized information on the archaeology of the Pueblo III period (AD 1150 to 1350) in various regions of the Southwest. This period postdated the decline of Chaco Canyon as a major regional center, and understanding it is important for understanding the relationship between Chaco and the modern Pueblos, as well as for understanding some aspects of Chaco itself.

Another period that is of perhaps even greater interest for understanding Chaco is the Pueblo I period (generally defined as AD 750 to 900, but see below), which immediately predates Chaco’s rise to regional dominance. I was therefore pleased to see the publication in 2o12 of Crucible of Pueblos: The Early Pueblo Period in the Northern Southwest, a volume synthesizing information on the Pueblo I period along the same lines as Adler’s effort for Pueblo III. It’s edited by Rich Wilshusen, Gregson Schachner, and James Allison, all of whom have made important recent contributions to understanding of this under-researched period. I’m just now getting around to reading it, and I decided to do a similar series of posts commenting on the chapters as I read them. I’m entitling the series “Foreshadow” to indicate the way developments during this period seem to, well, foreshadow later developments at and involving Chaco.

This post addresses the introduction, which is by the three editors of the volume along with Kellam Throgmorton, who is not otherwise a familiar name (at least to me) but who is thanked in the acknowledgments for his work “reimagining” this chapter. He was apparently a graduate student at the University of Colorado at the time, and has since graduated and is now “doing contract archaeology work in New Mexico.” The introduction as it stands is very engaging and readable, so if that was Throgmorton’s doing I can see why the volume editors took care to thank him specifically.

This introductory chapter is primarily a history of archaeological research on the Pueblo I period in the Southwest, but it also situates that history in the context of archaeological understanding of that period and how it relates to others, which has changed markedly over time. It also explains the reasoning for this volume’s use of “Early Pueblo” rather than “Pueblo I” to describe the period of interest, which is defined more broadly than Pueblo I has traditionally been. As with so much else in Southwestern archaeology, the issues here go back to the classification developed at the first Pecos Conference in 1927. As this chapter makes clear, this was initially primarily a developmental sequence rather than a chronological one, and the Pueblo I period in particular has been misunderstood on this account. This volume therefore uses a more general “Early Pueblo” period of circa AD 650 to 950 to frame the developments in the regions it discusses, which covers the various definitions that have been used for Pueblo I in different areas, as well as parts of Basketmaker III in some because of the importance of immediately preceding events for understanding Pueblo I.

The bulk of this chapter relates the history of understanding of the Pueblo I period by archaeologists. This history follows the familiar sequence of culture history/classification followed by processualism/environmental determinism followed by post-processualism/neohistoricism, but with an emphasis on how the Pueblo I period tended to be subsumed by larger theoretical constructs until the rise of large cultural resource management projects in the 1970s and 1980s massively increased the data available and forced a reevaluation of the period. The most influential of these efforts was the Dolores Project, which happened to occur in an area that was one of the most important centers of Pueblo I village development. The massive scale of this project, the largest ever in the US at the time, led to a much more detailed understanding of the Pueblo I period and the recognition that, rather than a brief interlude in the sequence of development from small hamlets to large pueblos, this was a time of rapid formation of the first major agricultural villages in the northern Southwest, followed by their equally rapid dissolution and a massive outmigration of people from the region. The precision of tree-ring dating allowed for very fine-grained understanding of the chronology, and the results of the project showed a level of dynamism in population movement and culture change that was totally unexpected and hard to fit in the gradual progression paradigm underlying the traditional Pecos classification.

Furthermore, certain aspects of the short-lived Dolores villages were strikingly reminiscent of the well-known Chacoan communities that emerged to the south shortly afterward, which led to the increasingly accepted idea that the formation and dissolution of villages during Pueblo I in the Dolores area were events that directly influenced the rise of Chaco. Indeed, it is now considered quite likely that many of the people who were involved in the development of early great houses at Chaco had moved there from Dolores.

So that’s the main message in this chapter, which also serves as an introduction to the volume itself and the other chapters in it. The next few chapters cover the specifics of settlement patterns in several parts of the northern Southwest, including not just the Mesa Verde region (the focus of most Pueblo I research so far) but also Chaco and its surroundings as well as areas further south and east. The latter two areas are often not addressed very well in research on this period, so I’m very interested in seeing the information on them presented here. The next few chapters cover a few broad thematic issues of interest for understanding this period across all the regions, then there are concluding chapters by Steve Lekson and John Kantner putting all this in a larger perspective. Overall this seems like a well-designed and desperately needed synthesis of an important but poorly understood period in Southwestern prehistory, and I’m eager to dive into the details.

Drones!

Looking East from Casamero Pueblo

Looking East from Casamero Pueblo

Unmanned aerial vehicles (UAVs), popularly known as “drones,” have become increasingly common in recent years as the technology behind them has developed. Some uses are controversial, such as military applications and uses that might violate privacy expectations or be dangerous to other aircraft, but other uses are more benign and can potentially open up new frontiers.

In archaeology, UAVs are increasingly being used for aerial photography and remote sensing in many places around the world. These are types of research that have been established for decades, but that until recently were prohibitively expensive for most archaeologists since they required both expensive camera equipment and the use of airplanes or helicopters. With the development of both lighter, less expensive cameras and UAVs that are robust enough to carry them, this type of research is now much more practical.

A recent paper by a team of researchers including Jesse Casana of the University of Arkansas and John Kantner of the University of North Florida reported on research using a UAV to take infrared thermal imagery, or aerial thermography, as well as color photography, of sites in the Blue J community south of Chaco Canyon, New Mexico. (Casana has the paper posted on his Academia.edu page.) Kantner has been studying Blue J and the surrounding area for several years and has come up with some interesting results.

Blue J is in an area at the southern edge of the San Juan Basin that is thick with Chacoan outlier communities, most of which date to fairly early in the Chacoan era and many of which were apparently abandoned while the Chaco system was flourishing. Casamero Pueblo is one site very close to Blue J where a great house has been excavated and is open to public visitation. These communities typically have one or more great houses and great kivas, and in fact it is unusually common for communities here to have multiple great houses compared to other Chacoan outlier communities. At Blue J, however, Kantner has so far not identified any great houses or great kivas. As he says on his website:

Turquoise, marine shell, jet, azurite, malachite, and other exotic materials attest to the success of Blue J’s inhabitants. Oddly, however, what was originally thought to be a great house turned out to be a normal residential structure, making Blue J the only community for miles around without Chacoan architectural influence.

Now, part of what’s going on here may have to do more with how archaeologists define “great house” than with anything about Blue J specifically. The function of the monumental buildings that have been given this label remains a point of active contention among scholars, with some arguing that they were primarily residential, perhaps housing community elites or religious leaders, and others arguing that they were non-residential public architecture, perhaps with ritual significance as sites of pilgrimage and/or communal feasting. Kantner belongs to the latter camp, so finding “normal” residential features at a suspected great house removes it from consideration as such, whereas another archaeologist might interpret such findings differently. (It’s worth noting that many if not most excavated “great houses” have showed at least some evidence for residential use, and in some cases they have not been noticeably different from other residential structures in a community except in size and location.)

The focus of the recent study was on demonstrating the potential for using UAVs to do fast, inexpensive survey of large sites and to identify buried features. Blue J is well suited for this on both counts. It is located at the foot of a steep cliff, which has resulted in many sites in the community being covered with substantial deposits of sediment carried by water and wind, making them difficult to identify on the surface. It is also fairly large for a Chacoan outlier community, with over 50 residential sites identified through previous surveys, which makes a fast method of survey over a large area an attractive proposition.

The study consisted of doing several flights with a UAV over the site, at different times of day and night, primarily with the infrared thermal camera to capture differences in temperature that are expected to be present between archaeological features and the dry desert soil. The original intent was to do some of the flights in the hottest part of the afternoon, but high winds ended up making this impossible. The results were nevertheless impressive: one site that had been previously identified through survey and limited excavation showed up clearly in the imagery, with buried walls visible in some of the images. Several other sites that had been identified but not excavated showed up as well, with buried walls again visible. A large circle showing a possible great kiva is particularly interesting given that no great kiva has yet been identified from surface survey.

Obviously further work is necessary to confirm some of the results from the imaging, but this is a very successful demonstration of the potential for this technology to improve survey and site identification so that further research can be focused on the most promising locations for sites. Other sensing techniques such as ground-penetrating radar have also been tried in the Southwest, but they are much slower and can be thrown off by some characteristics of the desert environment. Aerial thermography using UAVs offers another option that seems to have a lot of potential and it will be interesting to see how it is used as the technology continues to advance.
ResearchBlogging.org
Casana, J., Kantner, J., Wiewel, A., & Cothren, J. (2014). Archaeological aerial thermography: a case study at the Chaco-era Blue J community, New Mexico Journal of Archaeological Science, 45, 207-219 DOI: 10.1016/j.jas.2014.02.015

Orientation and Identity

Looking East from Peñasco Blanco

Looking East from Peñasco Blanco

Today is the winter solstice, which means it’s also the sixth anniversary of this  blog. On these anniversaries I like to write about archaeoastronomy, which is a very interesting topic and an important one for understanding Chaco and Southwestern prehistory in general. Last year I wrote about some research indicating that in the Rio Grande valley, an area generally thought to be outside the Chaco system but that was certainly occupied at the same time as Chaco, there was a long and very consistent tradition of orienting pit structures to the east-southeast, which is the direction of winter solstice sunrise. The winter solstice is very important in the cosmology and rituals of the modern Pueblos, so it makes a lot of sense that at least some Pueblo groups would orient their dwellings based on it.

As I noted at the time, this orientation is very different from that in the San Juan region to the west, including Chaco and Mesa Verde. In this area there is an equally long tradition of orienting pit structures to either due south or south-southeast. I’ve long wondered why this might be, and an article I read recently discusses the issue and proposes some interesting potential answers.

The article is by Kim Malville and Andrew Munro and was published in the journal Archaeoastronomy in 2010 as part of a special issue on archaeoastronomy in the Southwest. Malville is an astronomer who has done a lot of research on archaeoastronomy in the Southwest and identified many potential astronomical alignments, but this article is actually largely about debunking many of the alleged alignments claimed by others, particularly Anna Sofaer and her Solstice Project. Sofaer, an artist who turned her attention to archaeoastronomy after discovering the “Sun Dagger” effect involving a spiral petroglyph on Fajada Butte that on the summer solstice appears (or appeared) to be bisected by a “dagger” of light coming through a slit between large boulders in front of it. Sofaer went on to organize surveys of the major great house sites in Chaco Canyon to identify any celestial alignments in the orientation of their walls, and her team found that virtually all of them did show alignments to the positions of the sun or moon on solstices, equinoxes, or lunar standstills.

Light Snowfall on Fajada Butte

Light Snowfall on Fajada Butte

Sofaer and her collaborators went on to publish these findings widely, and to make a well-known documentary that has often been shown on television and inspired a lot of interest in Chaco. As Malville and Munro show in this paper, however, the evidence for these alignments is very thin. There is little to no justification in Pueblo ethnography for the idea of celestial building alignments, and the alignments themselves are identified with a substantial margin for error that makes spurious positive identifications likely, especially when so many potential alignments are tested for. Particularly concerning is how many of the alignments are to the minor lunar standstill, which is not a very impressive or noticeable event. (The major lunar standstill is a different story, and there is strong evidence at Chimney Rock in Colorado that the Chacoans were familiar with it and considered it important.) Malville and Munro also argue that the fact that most of the alignments are based on the rear walls of sites is also questionable, since there is no evidence that rear wall alignments were or are important culturally to Puebloans.

Instead, they argue that the alignments of rear walls are epiphenomenal, and that they mostly result from the more solidly established concern with the orientation of the front of a site. The bulk of the article is devoting to tracing these frontal orientations across time and space, with a primary focus on Chaco itself and on the earlier Pueblo I villages in the area of Dolores, Colorado that are often seen as being partly ancestral to the Chaco system.

As I noted above, there are two main orientations that persist through time in the San Juan region. One is to due south, and the other is to the south-southeast (SSE). With pit structures these axes are typically defined by a straight line of sipapu (if present), hearth, deflector, and vent shaft. There is often also a measure of bilateral symmetry between features on either side of this line, such as support posts. When there are surface rooms behind a pit structure, they often (but not always) conform to the same alignment, and when the back of a row of surface rooms is straight, it is typically perpendicular to the main orientation. Malville and Munro argue that these perpendicular back walls on many Chacoan great houses, which Sofaer has identified as having alignments to various astronomical phenomena, are really subsidiary effects of the main emphasis on frontal orientation.

The authors start their survey of orientations with the Basketmaker III pithouse village of Shabik’eschee at Chaco. Of 15 pithouses for which they could find adequate information on orientation, 11 faced SSE with an average azimuth of 153.7 degrees and 4 faced south with an average azimuth of 185 degrees. Strikingly, none of the pithouses showed any other orientation.

The north-south orientation isn’t difficult to understand, and Malville and Munro attribute it to use of the night sky for navigation (which would have been easy enough at this time even though there wasn’t actually a north star), and they also mention the widespread presence of Pueblo traditions mentioning origins in the north. While the exact reasons for adoption of this orientation may not be clear, its consistency isn’t unexpected since it’s pretty obvious and easy to replicate.

The SSE orientation, on the other hand, is a different matter. Note that at Shabik’eschee this was much more common than the southern orientation, from which it is offset by about 20 to 30 degrees in individual cases. There is more variation in this orientation than with the southern one (standard deviation of 7.7 degrees versus 2.4), but it’s sufficiently consistent and common that it seems like there must be some specific reason for it. Unlike the southern orientation, however, it’s not at all clear what that might be. Malville and Munro, sticking to their interpretation of orientations as references to places of origin, suggest that in the case of Shabik’eschee it might reflect the fact that some people might have migrated to Chaco from an area that was more to the north-northwest than due north, which seems implausible to me but then I don’t have a better explanation myself.

McPhee Reservoir, Dolores, Colorado

McPhee Reservoir, Dolores, Colorado

In any case, this pattern continues through time. The next set of orientations Malville and Munro look at are those of the pit structures at the Pueblo I Dolores villages. What they find is that SSE orientations are dominant here too, even more so than at Shabik’eschee. In fact, all of the pit structures they looked at had SSE orientations except those at Grass Mesa Village, which mostly faced faced south (although even here there were a few SSE orientations). This is in keeping with other evidence for differences in architecture among different villages at Dolores; Grass Mesa is known for having long, straight room blocks, as opposed to the smaller and often crescent-shaped roomblocks at McPhee Village, which with it is most often compared.

The Duckfoot site, to the west of the Dolores villages but contemporaneous with them, also had a SSE orientation. Further west, however, southern orientations become more common, including at the important village sites of Yellow Jacket and Alkali Ridge, plus some of the earlier Basketmaker II sites on Cedar Mesa in Utah.

There was one more orientation used during the Pueblo I period in the Northern San Juan region, however. At Sacred Ridge, in Ridges Basin near modern Durango, Colorado, the average azimuth of the pit structures is 120 degrees, the same east-southeast orientation corresponding to winter solstice sunrise so common in the Rio Grande. Malville and Munro remark on the similarity to the Rio Grande pattern and consider it “puzzling,” positing some potential ways that it could have come about. They argue, however, that wherever this pattern came from it didn’t last in the north, and they point to the extremely violent end to the occupation of Sacred Ridge as the end of this orientation tradition in the San Juan region (although this may not be strictly true, as discussed below).

From here Malville and Munro turn back to Chaco. Specifically, they look at the great houses at Chaco during its heyday from about AD 850 to 1150. Rather than pit structures, they focus on roomblocks, and they interpret the orientation of a roomblock to be the perpendicular to its long axis (in the case of rectangular roomblocks) or the perpendicular to the ends of the crescent of roomblocks with that shape. They find that most of the great houses have a SSE orientation, in keeping with the general trend throughout the region, as do the three northern outlier great houses of Chimney Rock, Salmon, and Aztec. Since this orientation is very close to the perpendicular of the minor lunar standstill moonrise alignment that Sofaer has proposed for many of these buildings, Malville and Munro argue that this widespread orientation explains the pattern much better than the lunar alignment. Pueblo Alto and Tsin Kletzin have north-south orientations, which is unsurprising since they lie on a north-south line with each other.

A few of the great houses have a more complicated situation. Peñasco Blanco appears to face east-southeast at an azimuth of approximately 115 degrees. This is intriguingly close to the Rio Grande/Sacred Ridge winter solstice orientation, which Malville and Munro do note. Although the unexcavated nature of the site makes it hard to tell for sure, it is possible that this is in fact an example of this orientation surviving much later in the San Juan region than the destruction of Sacred Ridge, although what, if any, connection there might be between the two sites is unclear.

Pueblo Bonito from Above

Pueblo Bonito from Above

And then there’s Pueblo Bonito. While the very precise north-south and east-west cardinal alignments of some of the key walls at this site are well known, it has also long been noted that there is evidence for different alignments and change over time here. Malville and Munro interpret the early crescent shape of the building as having a SSE orientation, and like many others they relate it to the similar size, shape, and orientation of McPhee Pueblo at McPhee Village. They then describe multiple stages of drift away from this orientation toward the cardinal orientation. There is surely something to this interpretation, but a careful look at the stages of construction of the site shows that the picture is probably more complicated. The very first construction at Bonito appears to have been straight and oriented to the south, and to have been incorporated later into the SSE-facing crescent. Subsequent building stages show evidence of both orientations having been present throughout the history of the building.

The complicated situation at Pueblo Bonito provides a convenient segue to the key issue here: what was driving this long-term but consistent variation? Why were two different orientations for buildings present in close proximity for hundreds of years, even as populations moved long distances and adjusted their cultures in profound ways? Malville and Munro suggest that these orientations may reflect longstanding cultural and ethnic diversity in the prehistoric Southwest. Given how long-lived and consistent these patterns are, they propose that they were related to deep-seated cultural identities. This is an intriguing idea that may allow tracking of specific cultural groups across the Southwest over centuries. It also provides another piece of evidence that Chaco Canyon was a multicultural community, and implies that even Pueblo Bonito itself contained groups with diverse backgrounds.

The picture is probably even more complicated than Malville and Munro suggest. They tend to implicitly assume that the orientations of pit structures are the same as those of the room blocks with which they are associated, but at least at Chaco this is not necessary true, particularly for small-house sites, which they also don’t address at all in this study. There are many examples of small houses where the room blocks are oriented to the east but the pit structures are oriented to the south (and possibly also SSE, although I haven’t checked this). This eastern orientation may reflect connections to the south, which have gotten a lot less attention in the literature than connections to the north although they appear to have been pretty important in the origins of Chaco.

In any case, I think this is fascinating stuff. It may not be archaeoastronomy per se, but it seems like a fitting way to mark the solstice.
ResearchBlogging.org
Malville JM, & Munro AM (2010). Cultural Identity, Continuity, and Astronomy in Chaco Canyon Archaeoastronomy, 23, 62-81

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