Thursday, July 18, 2019

Interview with Professor Steven Shackley, recipient of the Fryxell Award for Interdisciplinary Research

Professor M. Steven Shackley has recently been awarded with the prestigious Fryxell Award for Interdisciplinary Research. A symposium was held accordingly in his honour at the past Society for American Archaeology meeting in Albuquerque. But, this is not the only thing that is worth celebrating for Professor Shackley, as he has also turned 70 (belated happy birthday, Steve!) Here are the highlights of the conversation I have had with Professor Shackley. 

C: Carmen; S: Steve

C: First of all, congratulations on the Fryxell Award. How do you feel about the award and the symposium that was held in your honour in the past SAA meeting? 

S: It was very emotional for me. I got to hear about the incredible research that some of my former students have been working on. The symposium had brought old friends, colleagues and students together. This also provided the opportunity for some participants – whose regional specialisation do not normally overlap – to meet, discuss and generate new ideas and collaborations. Actually, Robin Torrence (Australian Museum) and Bruce Huckell? (University of New Mexico) met at the symposium and they are now collaborating in a new project.

Steve and all participants (except Bruce Huckell) of the session that was held in his honour at the past Society for American Archaeology meeting in Albuquerue (Photo courtesy of Steve Shackley).

C: Based on your long and successful research career, do you think the nature of lithic studies have evolved in the past decades?

S: Absolutely. Previous research on lithics focused largely on the metric measurement, but the works being conducted by me and my colleagues have demonstrated the potential of geochemical analysis in lithic studies, especially in terms of reconstructing patterns of resource procurement, trade and exchange. If you go through the journal Lithic Technology, you will notice the trend of using more research using science in lithic studies in the recent decades. 

C: Since you specialise in lithic, particularly obsidian, I do have an obsidian-related question to ask. Do you watch the ‘Game of Thrones’?

S: Yes.

C: So, what is your opinion on the ‘dragonglass’ in the final series? I am asking because it seems to have touched the nerves of a lot of my archaeologist friends who specialise in lithics. The opinion on the matter seems to have been half and half. 

S: Haha...I like it, mostly because it has drawn the general public’s attention to obsidian. I wonder why the producers of the show picked obsidian as their choice of dragonglass. Actually, I am working on a popular book on obsidian. What bothers me is they went great length to look for this dragonglass; but when it came to the actual killing of the Night King, Arya pulled out another dagger instead, at least that's what it looked like on the screen.  

C: Back to more serious questions, tell us about how did you get into archaeology or anthropology?

S: I grew up in the rural area in California. When I was 14 years old, I got a job to mend the fences of these large ranches that spanned over 14 square miles. There were these projectile points scattered on the ground within these ranches. I found these projectile points very fascinating, which inspired me to choose to study geology in college. Unfortunately, the war broke out not long after I started college, so I was into the Marine Corps and stationed in Vietnam. When I came back from the war, I used the ‘GI Bill’ to finish my college education, graduating with double majors in geology and anthropology. I continued to pursue a Master in Anthropology. After that, I went into the field of Cultural Resources Management (CRM). However, the funding for CRM was severely reduced during the presidency of Ronald Reagan. This had urged me to go back to graduate school to obtain a PhD in Anthropology.

Steve and the La Union ash flow tuff obsidian source in Honduras in 1998 (Photo courtesy of Steve Shackley).

C: I can see that you were trained in both disciplines – geology and anthropology – do you think we have made enough progress in developing archaeological science into truly interdisciplinary? 

S: This question makes me think of the discussant chapter that Rosemary Joyce wrote for my book ‘X-Ray Florescence Spectrometry (XRF) in Geoarchaeology’. Some people may find it strange that I asked Rosemary Joyce, who is known for her post-processualist approach, to write the introduction of a scientific volume; but, very few people know that she actually had a major in mathematics. Precisely because of this, she was capable of summing up the value of science in archaeological research by commenting that many of the 21stcentury questions we archaeologists are asking can best be addressed through archaeological science.

When I first started applying scientific methods in archaeological research, only a few archaeologists had a background in science. Then, in the 60s and 70s, there was a boom in the applicability of different analytical techniques. In a way, the later post-processual theories were being developed in response to this increasing emphasis on science in archaeology, although few would have admitted it then. Nowadays, science has become an integral part in archaeological research, especially so when the portable analytical methods are getting cheaper and better in terms of detection limits and accuracy. These developments have definitely encouraged researchers to be more willing to incorporate certain scientific elements in their research. Some may even argue that since the technology is getting better and better, we do not even need to have a background in science to conduct analysis. This is a very dangerous approach! We have to be careful when it comes to producing data; and even more careful when it comes to interpreting the data. 

In answer to your question, I think there is definitely better integration between science and theory in archaeological research now than before, but things can be better still. 

C: What is your advice for students who would like to undertake studies in lithics or geochemistry? 

S: Don’t be afraid of science! The research environment is getting more and more competitive, with fewer academic jobs per capita.  Having a background in a science field, whatever that might be, has helped my students procure academic employment.  Even in government it seems more important than in the past.  As the world becomes increasingly technological, for good of bad, it will increasingly be an requirement for archaeologists to have a science background.  Whether academic programs will recognize this or not is still not clear.

C: When I was browsing through your CV before the interview, I notice that you are currently listed as the Director of the Geoarchaeological XRF Laboratory. Can you tell us more about this new venture? 

S: I helped the company that sells the Thermoscientific Quant’X Energy Dispersive X-Ray Fluorescence to set up systems all over the US and Canada. When I retired, the company offered me a discount on purchasing the XRF instrument. I took my chance, bought a Quant'X XRF instrument, and then moved to Albuquerque to set up my laboratory because it is more convenient for me to sample and analyse the obsidian sources here. 

I collaborate with researchers from different disciplines, such as archaeology, chemistry and geology, but I also work with the non-academic sector. This allows me to get involved in very diverse and interesting projects. For example, I work with a company that produces cement. The cement that is poured at different time of the year should have different composition because the cement reacts with the environment. This is why we work together to monitor any changes in the composition and to make sure that the recipes for the mix are as accurate as possible. Recently, I also got an opportunity to work with a retired architect on analysing the glass that covers these 19thcentury photographs. Most of the glass at this period was produced in France, which would have given a slight purplish taint. The analysis of the glass points to the glass source in Pennsylvania. 

C: Sounds like you have a very packed schedule, do you have any time to relax?

S: Yes. I’ll go on to geological field trips from time to time. I am also a drummer in a band. We mostly play covers of rock and blues music. Actually, the beginning of my band career can be traced back to high school. After that, when I was in the Marines, a couple of us formed a band called the ‘Green Machine’ in Da Nang. We used to play in different clubs in Vietnam. My granddaughter thinks I am really cool!

In case you would like to discover this artistic side of Steve, go visit his YouTube channel! Here’s the link: 

Monday, July 1, 2019

Forum: Funding opportunities and the prospect of archaeological sciences around the world

The Forum is a new initiative of the bulletin, in which we will discuss some of the hot topics that have been going on in archaeological science. To kick this new initiative off, we are investigating the funding opportunities and the prospect of archaeological science around the world. In this first round, we have contributions from Professor Aubrey Cannon (Professor, McMaster University) and Dr Andrew Roddick (Associate Professor, McMaster University) and Dr Siran Liu (Research Associate, University of Science and Technology Beijing) to tell us more about the situations in Canada and China respectively. 

Infrastructure and Innovation in Canadian Archaeological Science 

Aubrey Cannon and Andrew P. Roddick
A number of pioneering developments in archaeological science began in Canada, several with far-reaching implications. For example, Erle Nelson (2010), a graduate of McMaster University’s Physics department, developed AMS radiocarbon dating at the McMaster Nuclear Reactor in 1977. The reactor, which first became operational in 1959, continues to be used in the chemical characterization of archaeologically recovered materials (see for instance, MacDonald et al. 2011 and Michelaki et al. 2012). Henry Schwarcz(Department of Geography and Earth Sciences, McMaster University), was also instrumental in sustaining the growth and development of archaeological science. His work, which focused on uranium series and electron spin resonance dating and later the stable isotope analysis of biological tissues (summaries in Schwarcz 1997 and Schwarcz and Schoeninger 2011 respectively), has helped establish a national baseline for archaeological science in Canada.

The prospects for archaeological science in Canada changed significantly in 1997, with the development of the Canada Foundation for Innovation (CFI), which resulted in less direct dependency on the labs and faculty of science departments. The Canadian government created CFI to enable researchers to develop and equip state-of-the-art research facilities, and to support initiatives that break new ground or apply existing instruments in new ways. CFI’s first Chair, Dr. David Strangway (previously at the University of British Columbia) insisted its resources would go beyond Science, Medicine, and Engineering departments, and also be made available to researchers in the humanities and social sciences. In its first 20 years, between 1998 and 2017, a total of 43 CFI grants were awarded across 15 Canadian universities in support of specialized archaeological science lab facilities and equipment for ceramic, lithic, zooarchaeological, paeleoethnobotanical, osteological, isotopic and ancient DNA analyses (Fig. 1).

Figure 1. Number of Canadian Foundation for Innovation (CFI) grants for archaeological science across Canada from 1998 through 2017. 
The CFI program has generated new research questions, particularly since researchers, their instruments, and the pasts they bring to light are inseparable (Barad 2007). At their best, these laboratories are “scenes of disciplined seeing” (sensu Dennis 1989: 342), where analytical tools and techniques, including those of modern ceramic analysis and paeleoethnobotany can produce radically new ways of observing, representing, and knowing the past for both established scientists, but also undergraduate and graduate students. Indeed, the financial support of CFI is contingent on an accounting of thenumber of highly trained personnel directly attributable to the infrastructure. A parallel initiative, also sponsored by the Canadian federal government, has also provided funding to support the hiring and retention of leading researchers in archaeological science. The Canada Research Chairs Program (CRCP) was designed in 2000 to attract and retain some of the world’s most accomplished and promising researchers, including archaeologists (see for instance, Dr. Michael Richards, a Tier 1 CRC in archaeological science at Simon Fraser University). CFI and CRCP are highly competitive, and have primarily supported scholars in Health, Science and Engineering; archaeology has received only the tiniest fraction of the $6.6 billion allocated by CFI in its first 20 years. Nevertheless, Canadian archaeologists are becoming more adept at developingapplications, tailoring their requests to fit the priorities of these programs, resulting in a significant growth in Canadian archaeological science. 

The sometimes-lengthy dialogue between physical scientists and anthropological archaeologists continues across Canadian university campuses and the private sector. Physical scientists listen to anthropological archaeologists and grapple with their objectives. Anthropological archaeologists work with physical scientists to craft anthropologically based questions that work within the limits of current methods and facilities. The Social Sciences and Humanities Research Council of Canada (SSHRC), the main federal government funding body for social science research, has developed programs explicitly designed for such dialogues. SSHRC encourages interdisciplinary communication and cooperation and the development of new research capacities with Research Development Initiatives grants and Connection grants. SSHRC is also the primary source of broader archaeological funding in Canada, and researchers often develop these grants in tandem. For instance, it is common to incorporate infrastructure facilities and highly trained personnel developed through CFI-funding, and to transform initial interdisciplinary collaborations from Connection grants into larger-scale SSHRC projects. Archaeological science is also flourishing outside the academic arena, where collaborations are developing with private-sector cultural resource managements firms. This is bringing new, added value to the space where most archaeology happens in Canada (Martindale et al. 2019, Pfeiffer et al. 2014). 

All these initiatives have helped foster a culture of science-based archaeological research, methodological innovation and inter-disciplinary collaboration across the country. Although there is some concern about SSHRC funding initiatives and programs as public and government priorities change, support for innovative collaborations remains. The CFI and CRC programs have been especially successful and resilient to changing government priorities. Although archaeology’s access to these programs remains modest in comparison to their overall scale and scope, they continue to expand and create new opportunities. At this time, the future of archaeological science in Canada continues to look very bright.

References cited
Barad, K., 2007. Meeting the Universe Halfway. Duke University Press, Durham, NC.
Dennis, M. A., 1989. Graphic Understanding: Instruments and Interpretation in Robert Hooke’s Micrographia. Science in Context 3(2), 309-64.
MacDonald, B. L., R.G.V. Hancock, A. Cannon, and A. Pidruczny, 2011. Geochemical Characterization of Ochre from Central Coastal British Columbia, Canada. Journal of Archaeological Science 38(12), 3620-30.
Martindale, A., G.T. Cook, I. McKechnie, K. Edinborough, I. Hutchinson, M. Eldridge, K. Supernant, and K.M. Ames, 2018. Estimating Marine Reservoir Effects in Archaeological Chronologies: Comparing ΔR Calculations in Prince Rupert Harbour, British Columbia, Canada. American Antiquity 83, 659–680.
Michelaki, K., R.G.V. Hancock, and G.V. Braun, 2012. Using Provenance Data to Assess Archaeological Landscapes: An Example from Calabria, Italy. Journal of Archaeological Science 39(2), 234-46.
Nelson, E., 2010. Personal Recollections of a Good Experiment. Radiocarbon 52(02), 219-27.
Pfeiffer, S., R.F. Williamson, J.C. Sealy, D.G. Smith, and M.H. Snow, 2014. Stable Dietary Isotopes and mtDNA From Woodland Period Southern Ontario People: Results from a Tooth Sampling Protocol. Journal of Archaeological Science 42, 334-345.
Schwarcz, H.P., 1997. Uranium Series Dating. In Taylor R.E., Aitken M.J. (eds), Chronometric Dating in ArchaeologyAdvances in Archaeological and Museum Science, vol 2. Springer, Boston, MA., pp. 159-82. 
Schwarcz, H.P. and M.J. Schoeninger, 2011. Stable Isotopes of Carbon and Nitrogen as Tracers for Paleo-Diet Reconstruction, in: M. Baskaran (ed) Handbook of Environmental Isotope Geochemistry. Springer-Verlag, Berlin, Germany, pp. 725–743.

The future of archaeological sciences in China

Siran Liu

There are a number of funding opportunities for archaeological scientists working in China. Previously, the State Administration of Cultural Heritage provides the most important and stable funding for archaeological science in China. Unfortunately, it had stopped and now focuses only archaeological excavation and conservation. The National Natural Science Foundation of China (NSFC) is currently the most essential one. It supports scientific research projects from eight divisions (Mathematics/Physics, Chemistry, Biology, Earth Science, Engineering and Material Science, Information science, Management science and Medical Science). Archaeological scientists can find various relevant topics within these divisions from the study of human evolution to the development of cutting-edge scientific tools for analyzing ancient artefacts. The competition is however quite severe and only a very small proportion of applications will finally be granted. The National Social Science Foundation of China is another choice. It has funds dedicated for archaeological research projects but only increased the support for archaeological science in recent years. The Ministry of Education and provincial governments also have their own funds for natural and social science research, and archaeological scientists can try their luck there. The Ministry of Science has funded several major projects of archaeology in the last two decades such as the “The Origin of Chinese Civilization Project” and “The Xia-Shang-Zhou Chronology Project”, and archaeological scientists were deeply involved and benefited from these projects. There also several other funding sources for archaeological scientists such China Postdoc Science Foundation and research funds from universities and academic institutes. Crosswise projects are usually smaller than the aforementioned ones but play an increasingly important role for archaeological scientists. The PIs of archaeological projects and museum curators can channel part of their funds to labs for dating, artefacts characterization, in-situ analysis as well as technical supports in field. However, it is still not a very common practice since previously most archaeological scientists managed to find funding by themselves (mostly from government projects). In addition, many of these collaborations are not well designed in advance and sometimes archaeological scientists are just providing services without actively engaged in the project. In contrary to US and UK, non-governmental organizations provided little support in archaeological research. In general, the archaeological science is relatively well funded and most researchers have enough funding to run their analyses. But in my opinion much more resources should have been invested on developing the discipline itself to create new analytical methods and raise new research questions, rather than repeatedly analyzing the same type of materials. In order to do this, the government-operated foundations (e.g. NSFC) should provide funding dedicated for archaeological science research, encouraging scholars to explore new possibilities. Meanwhile, the evaluation of funding applications should be conducted by experts from this field rather than randomly selected scientists working on totally irrelevant topics. 

Tuesday, June 18, 2019

More on the R.E. Taylor Student Poster Award at the 84th Society for American Archaeology Annual Meeting, 10th - 14th April 2019, Albuquerque, USA

And the winner goes to...

Regional Production and Trade of Glazed Ceramics in Medieval Central Asia along the Silk Road
Catherine Klesner, Brandi L. MacDonald, Pamela B. Vandiver
The Silk Road, the dynamic trade route connecting East Asia to the Mediterranean, transported not only material goods, but also facilitated the transmission of artistic styles, languages, religions, and technologies. The trade route, often referred to as the plural Silk Roads due to the continually shifting and complex character of the exchange networks encompassed in the term (Fig. 1), crossed the mountains, desert, and steppes of Central Asia. Beginning in the 6th c. CE, as trade intensified over the northern branch of the Silk Road, there was accelerated growth of urban centers along the northern edge of the Tien Shen mountains. Archaeological sites from this time provide valuable insights into this trade as well as the economies and technologies of the supporting communities. By examining the material remains, we can reconstruct ancient trade and knowledge networks. Glazed ceramics, while only a small proportion of ceramic assemblages (10%) from urban Central Asian sites in the Medieval Period, relay important information about trade and ceramic production technologies in these Silk Road cities (Henshaw 2010).
Figure 1. Location of the seven medieval cities whose ceramics are sampled in this study in relation to the sites in the NAA databases produced at MURR and the Lawrence Berkeley National Laboratory of Nuclear Archaeology (LBL). The chemical compositions of the pastes were compared to the Kazakh ceramics to place them within a wider Asian context. The combined datasets were composed of samples from China (n=161), Iran (n=928), Iraq (n=198), Kazakhstan (n=61), and Uzbekistan (n=8).

Glazed ceramic production was an important and dynamic technology in the Islamic world (Mason 1995) with many innovations occurring in ceramic technologies during the Islamic period. Ceramic technological innovation was a significant element for economic competition in the long-distance trade networks of the Silk Road (Mason 1995). In Central Asia local traditions and technologies continued to develop as a result of increased contact with nonlocal goods, peoples, and technologies.  For instance, Islamic potters responded to imported ceramics by not only making imitations of the non-local wares for local consumption, but also by innovating several glazing techniques, including lustre decoration and polychrome underglaze painting, which in turn influenced the decoration employed by Chinese potters (Tite 1988; Mason et al. 2001). The rise of lead-glazed ceramics in Southwest Asia can be linked to attempts to replicate imported Chinese wares traded along the Silk Road (Tite 1988; Hill et al. 2004; Wood et al. 2007; Henshaw 2010). 
This research characterizes the provenience of finely decorated glazed pottery and specialty ceramics from Central Asia to determine the scale of local production and technological innovations and attempts to understand the stylistic models for local development provided by long distance trade of ceramics from the 9-15th c. CE. The ceramic sherds in this study, including both glazed (n=39) and unglazed ceramics (n=67), were excavated from seven medieval sites (Fig. 1), Aktobe, Aspara, Bektobe, Kastek, Kulan, Lower Barskhan, and Tamdy. The ceramic bodies and glazes on the 106 samples were analyzed by two analytical techniques: laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and neutron activation analysis (NAA)..LA-ICP-MS was used to characterize trace elements both the pastes (n=106) and glazes (n=40), and NAA characterized the pastes (n=103). 
Figure 2. Ceramics in Paste Groups 2, 3, 6 and 8.
Number of samples
Ceramic Type
Geographical Distribution 
Taraz region 
All 11-12th century sites
Eastern Sites 
Tamdy, Bektobe, and Kastek
Kulan and Aktobe
Western Sites 
Table 1. Results of NAA compositional analysis and geographical distribution.193% of samples in Group 5 come from Aktobe, with one sample each coming from Bektobe and Kastek.

Compositional analysis of the ceramic pastes by NAA indicates that there are three distinct compositional groups for the lead-glazed ceramics, and five compositional groups of unglazed ceramics (Table 1). These groups were then compared to NAA data of more 1300 previously analyzed ceramics from Southwest Asia, Central Asia, and China, as seen in Figure 1 (Klesner et al. 2019). Groups 3 and 6, were likely made in Southwest Asia (Iran) and imported into the region through Silk Road Trade. Additionally, Group 8, which is composed of high-fired spheroconical stoneware vessels were also likely made in Southwest Asia. Group 2, which was only found at the site of Aktobe, was likely locally produced. This compositional study indicates that there was local production of lead glazed ceramics in the style of ceramics typical throughout the Islamic world in Central Asia as early as the 9 - 10th c. CE. However, while there was a local production of glazed vessels, there was still active long-distance trade in glazed finewares and specialty ceramics (spheroconical vessels) throughout the Medieval Period. 
Henshaw, C. M., 2010. Early Islamic Ceramics and Glazes of Akhsiket, Uzbekistan. PhD Dissertation, Department of Archaeology, University of College London, London, UK. 
Hill, D. V., R. J. Speakman, and M. D. Glascock, 2004. Chemical and Mineralogical Characterization of Sasanian and Early Islamic Glazed Ceramics from the Deh Luran Plain, Southwestern Iran, Archaeometry4:585-605. 
Klesner, C., and B. L. MacDonald, L. Dussubieux, Y. Akymbek, P. Vandiver, 2019. Compositional Analyses of Early Islamic Glazed Ceramics from Southern Kazakhstan by NAA and LA-ICP-MS accepted article, JAS: Reports.
Mason, R. B., 1995. New Looks at Old Pots. Muqarnas 12, 1-10.
Mason, R. B., M. S. Tite, S. Paynter, and C. Salter, 2001. Advanced in Polychrome Ceramics in the Islamic World of the 12th Century AD, Archaeometry 43, 191-209. 
Tite, M. S.,  1988. Inter-Relationship Between Chinese and Islamic Ceramics from 9th to 16th Century AD. In: Proceedings of the 26th International Archaeometry Symposium Held at University of Toronto, Toronto, Canada, Edited by R. M. Farquhar, R. G. V. Hancock and L. A. Pavlish, Toronto, pp. 30-34. 
Wood, N., M.S. Tite, C. Doherty, and B. Gilmore 2007 A Technological Examination of Ninth-tenth century AD Abbasid Blue-and-White Ware from Iraq, and its Comparison with Eighth Century AD Chinese Blue-and-White Sancai Ware. Archaeometry 49(4), 665-684.

Thursday, June 13, 2019

R.E. Taylor Student Poster Award at the 84th Society for American Archaeology Annual Meeting, 10th - 14th April 2019, Albuquerque, USA

Eunice Villasenor (Arizona State University) and Rachel Cajigas (University of Arizona) are the honourable mention of the R.E. Taylor Student Poster Award. Here's the summary of their awarding winning research.

The Distribution and Characterization of Agricultural Terraces on Cerro de la Mesa Ahumada, Mexico
Eunice Villasenor Iribe, Christopher T. Morehart, and Andrés Mejia
This poster presents the preliminary results of research conducted on the agricultural landscape modifications of Cerro de la Mesa Ahumada, a medium sized mountain that is located between the northern Basin of Mexico and the southern Mezquital valley. Located on the top of this mesa is the Epiclassic (600-900 AD) archaeological site known as Los Mogotes. Evidence of occupation is present in the form of large residential and ceremonial structures, terraces, and water reservoirs. Some of these features have been excavated as part of the Northern Basin of Mexico Historical Ecology Project being conducted by Dr. Christopher Morehart. 
Prominent features of this mesa are the terraces found throughout the mesa (Fig. 1). Terrace systems are also found throughout the surrounding hillslopes and region. Terraces are used not only for agricultural purposes but are often used to build level platforms for the construction of residential and ceremonial structures. Using ground survey, aerial geographical survey, and excavation it was determined that terraces found within the site were used agriculturally as well as structurally. To better understand the terraces found on this mesa it was important to collect multiple types of data by using different methods. Documenting the extent, distribution, and chronology of the terraces is essential to understanding the connections between anthropogenic landscapes, agricultural production, and demography. 
Figure 1. Terraces in Los Mogotes (taken by Christopher Morehart).
In this poster we present several lines of data to better refine our understanding of the terraces: GIS maps made using satellite data; topographic data collected with total stations; GPS data from ground survey; topographic data produced using drones; and excavation data.  These combined lines of data allow us to propose preliminary interpretations of form, function, distribution, and chronology of the terraces and their role in the ancient economic systems of the hills’ inhabitants. For this poster, we were most interested in determining the characteristics, distribution, and possible productivity of the terraces found within the mesa top. 
To first establish the distribution and characteristics of the terraces, a diverse range of data were used to create a map of the terraces on the mesa. Terraces were mapped (Fig. 2) and analyzed in Arc GIS using .40 cm VHR GeoEye-1 data, GPS data, and topographic data collected. This mapping resulted in 1352 features of which some may be connected to form larger linear terraces. Once terraces were mapped the characteristics of terraces such as slope and aspect were evaluated. Through the use of 5m LiDAR data, it was possible to determine the slope and aspect of terraces. Slopes ranged from 0 -  ̴40 % slope. After determining the slope of the mapped features, we were able to calculate the average % slope of the mapped terraces, which yielded an average of 13.20 % slope (Figure 3). After determining the average slope of mapped terraces, the aspect prevalence was determined. Through this analysis, we discovered that a majority of terraces are constructed with a dominantly easterly prevalence. It is likely that the slope and aspect were important factors in determining where terraces were constructed. If it is accepted that a majority of the terraces mapped were used for agricultural purposes then it is likely that these characteristics impacted productivity in some way. 
Figure 2. Satellite image of Cerro de al Mesa Ahuamada with mapped terraces in white.

The % slope average calculated is similar to the upper limit of 15 - 20 % slope used by Hirth (2000) as the maximum range of where terraces are constructed in Mesoamerica. Due to the large range of slope determined for the terraces on this mesa, we decided to use the average slope increased by one standard deviation (6. 25 % slope) to determine the range of likely agriculturally productive terraces.  Using the distribution map created we determined areas of agriculturally productive terraces. Based on a review of previous estimates of terrace use limits (Hirth 2000), we determined that the range of productive and useful agricultural terraces most likely was constructed in a slope with a range of 0 -   ̴20 % slope (Fig. 3). This range of slope covers the tops of the mesa and results in an area of 402.35 ha of potentially cultivable land. To determine the potential productivity of this area using terraces we conducted calculations based off of previous estimates of productivity of maize for upland rainfed zones in Mexico (Hirth 2000; Sanders 1976).  To simplify this estimate, we decided to limit cultivable crops to just maize. Using the estimates mentioned above to create a calculation of productivity, it was concluded that the potential production is scarcely sustainable for the current population estimates, 750-1000, for the site of Los Mogotes (Parsons 2008). If an annual fallow cycle is considered as part of the production process, then sustainability of maize production for this mesa top is even less likely sustainable for the estimated population. 
Figure 3a. Percent slop distribution of all mapped terraces.
Figure 3b. Percent slope distribution of mesa top terraces with percent slope <20%.
The productivity estimates presented in this poster were greatly simplified and future work will broaden some of the assumptions used. Further floral analysis of the soil samples retrieved from the agricultural terraces will provide a more accurate representation of the agricultural profile. Excavation has occurred for one agricultural terrace (Villasenor Iribe and Morehart 2019), but future excavations are also planned that will provide a better understanding of the construction methods for agricultural terraces. The new data collected will also be useful in creating more accurate estimates for the productivity of terraces. This type of research explores not only the characteristics of agricultural productivity but also the economic and political systems that are at work to create such large modifications of the landscape. This research may also be useful in studying regional agricultural changes as part of macroscale political changes. 

References cited
Hirth, K., 2000. Archaeological research at Xochicalco. Salt Lake City: University of Utah Press.
Parsons, J., 2008. Prehispanic Settlement Patterns in the Northwestern Valley of Mexico: The Zumpango Region. Museum of Anthropology Memoirs, No. 45. University of Michigan, Ann Arbor.
Sanders, W., 1976. Agricultural History. In The Valley of Mexico: Studies in Pre-Hispanic Ecology and Society. Albuquerque: University of New Mexico Press
Villasenor Iribe, E., and Morehart, C. (2017). Proyecto de ecología histórica del norte de la cuenca de México, informe de 2018. Informe enviado al Instituto de Antropología e Historia d México, CDMX.

Early Agricultural Practices at La Playa, Sonora, MexicoA Multi-Scalar Geoarchaeological Study of Prehistoric Earthen Irrigation Canals

Rachel Cajigas

Earthen irrigation canals were an important technological development in arid lands farming. The earliest farmers on the floodplains of the Sonoran Desert used careful planning, group cooperation, and experimentation to create productive agricultural landforms. The diversity in size and complexity of Early Agricultural period (2100 B.C.–A.D. 50) farming communities requires examination of the specific factors that favored this significant investment in landscape modification in order to understand the development of these practices. The examination of local environmental conditions and their relationship to the timing of agricultural practices is key in understanding the regional development and demise of early earthen irrigation canals.

La Playa is located in Sonora, Mexico (Fig. 1). This area has important implications on the understanding of the development of agricultural techniques because it is the single largest Early Agricultural period site in the Southwest U.S./Northwest Mexico region. This geoarchaeological research examines when and under what environmental conditions this technology was developed and abandoned. 

Figure 1. Map showing the area of La Playa

A multi-scalar, multi-technique geoarchaeological methodology was employed to investigate the canals at La Playa and resolve the timing of use and abandonment of the canals and determine how they articulate with floodplain environmental conditions. These methods are organized into three phases to accomplish these research goals.

Phase 1: Reconstruct spatial extent of canal system - Pedestrian Survey and GPS Documentation, Satellite Imagery and GIS Analysis, and Magnetic Gradiometry
Phase 2: Characterize depositional conditions - Particle Size and Thin Section Analysis
Phase 3. Constrain the timing of canal network - Accelerator Mass Spectrometry (AMS) 14C and Optically Stimulated Luminescence Dating (OSL)

Modern erosion is actively destroying the La Playa site (Fig. 2), highlighting the urgent need for documentation of archaeological features. In areas that have been highly eroded, much of the archaeology and irrigation canals have been destroyed. As much as 50% of the site is estimated to have been eroded. 

Figure 2. Map of La Playa showing the areas where samples were taken.

Some areas of the site have been affected by low-energy sheet wash erosion. In these areas, wind or water have winnowed away fine, silty sediments, leaving behind larger clasts, such as fire-cracked rock that lined the irrigation canals. Fire-cracked rock was likely used in canals to slow water velocity and prevent erosion during use. In some areas of the site, concentrations of fire cracked rock from eroded canal remains are so dense they are visible in the satellite imagery. 

Using high resolution satellite imagery, the remains of approximately 10 km of irrigation canals were documented in eroded areas of the site. An additional 2 km of canals were documented during pedestrian survey using a GPS (Fig. 3).

Figure 3. Map showing the irrigation canals.

In order to examine intact canals, magnetic gradiometry was used to detect canals buried below the floodplain surface in areas that had not yet been eroded. 3 km of buried canals were detected, as well as agricultural fields and several circular structures. Magnetic data were georectified using ArcGIS and UTM coordinates were generated to locate canals. Thirteen trenches were excavated to examine canal stratigraphy and collect samples for particle size analysis, thin section analysis, AMS 14C and OSL dating.

Stratigraphic information suggests that low-energy depositional conditions made the floodplain environment suitable for farming. Particle size analysis showed that the canal sediments and associated soils were fine in texture with very little variation. Thin section analysis on soils surrounding canals indicate these soils were saturated with water and composed of fine sediments with organic material.

AMS 14C and OSL dates on canals corresponding to the early and late portions of the Cienega phase (800 B.C.–A.D. 200) of the Early Agricultural period, which is the period of peak occupation at the site. These dates also corresponds to the earliest direct dates on maize at La Playa (A.D. 20–240) (Carpenter et al. 2015). Deep erosion of the floodplain occurred after A.D. 350, and there is no evidence of subsequent canal use. 

In sum, this research documented 15 km of irrigation canals that are at risk of erosion. These canals were in operation during a period of low-energy floodplain deposition that created a wetland environment conducive to agriculture. Earthen irrigation canals were used until A.D. 350 when severe floodplain erosion occurred. Although the site was not abandoned at this time, there was a sharp drop in site use (Copeland et al. 2012). 

The precise chronology of the spread of agricultural technology across the Southwest U.S./Northwest Mexico is disputed. The earliest known maize in the Southwest dates ~2100 B.C., but the earliest known canals were constructed much later, by ~1500 B.C. in the Santa Cruz river valley (Herr 2009). Prior to this geoarchaeological research, canal systems in northern Sonora were not closely examined. This research helps to address this gap in the regional approach to documenting the development of irrigation technology. La Playa shows agricultural intensification occurring later than similar Early Agricultural period sites in the Tucson Basin to the north. This is compelling evidence that the development of irrigation technology in the southwest US/northwest Mexico is more complex than simple northward diffusion models.

References cited
Cajigas, R., 2017. An Integrated Approach to Surveying an Early Agricultural Period Landscape: Magnetic Gradiometry and Satellite Imagery at La Playa, Sonora, Mexico. Journal of Archaeological Science: Reports 15, 381–392.

Carpenter, J.P., Sánchez, S., Watson, J. and Villalpando, E., 2015. The La Playa Archaeological Project: Binational Interdisciplinary Research on Long-Term Human Adaptation in the Sonoran Desert. Journal of the Southwest 57(2), 213–264.

Copeland, A., Quade, J., Watson, J., McLaurin, B., and Villalpando, E., 2012. Stratigraphy and geochronology of La Playa archaeological site, Sonora, Mexico. Journal of Archaeological Science 39, 2934–2944.

Herr, S.A., 2009. The Latest Research on the Earliest Farmers. Archaeology Southwest 23(1), 1–3.

Mabry, J.B., 2008. What's so Archaic about the Late Archaic? Recent Discoveries in Southwestern North America. The SAA Archaeological Record 8(5), 36–40.