2021 Recipient: Mikayla Rosario

2022 Society for California Archaeology Conference

Mikayla presents her poster at the 2022 Society for California Archaeology Conference

Mikayla presents her poster at the 2022 Society for California Archaeology Conference

The Society for California Archaeology (SCA) Annual Meetings serve as platforms to share recent and ongoing archaeological research in California. I used my funds from the AURG to attend the 2022 Annual Meeting, where I presented a poster on research I conducted in the Archaeometry Lab. I attended the meeting with fellow undergraduate student Morgan Hall, and graduate students Diana Malarchik, Marcela Barron, and Jessica Morales.

            We all arrived at the conference after the first rounds of talks had finished, so Morgan and I volunteered to help sell publications from the Center for Archaeological Research at Davis (CARD). We then attended the silent auction, which took place in a large room lined with tables staffed by representatives from CRM firms, government agencies, and other organizations which employed archaeologists. The silent auction provided an opportunity to mingle, network, and drink, and by the end of the night our bags and pockets were stuffed with business cards, candy, and free merchandise.  

            The next morning, we participated in the first annual SCA Ethics Bowl, where teams of students compete to effectively address ethical dilemmas that commonly arise in archaeological careers. As soon as I saw that the opposing team had matching outfits and stacks of notes, I knew our chances of winning were slim. As anticipated, we didn’t win, but it was still an interesting experience.

            The group then attended a symposium organized by Dr. Jelmer Eerkens, my faculty advisor. Diana presented on her research which focused on heavy metal levels in pre- and post-contact Ohlone populations, and Dr. Eerkens discussed how stable isotope analyses can be used to inform on weaning and dietary practices.

            That afternoon, Morgan and I presented our posters. We set up in a small room with five other presenters, whose poster topics ranged from landscape reconstruction to toolstone procurement. My poster, titled “Paleodietary Life Histories at Ayttakiš ‘Éete Hiramwiš Trépam-tak (CA-ALA-677/H) based on Stable Isotope Signatures,” focused on research done in collaboration with the Muwekma Ohlone Tribe, Far Western Anthropological Research Group, and CalTrans. This research involved conducting carbon and nitrogen stable isotope analyses on collagen extracted from small bone fragments from 19 individuals (dating 722–597 cal BP) from ALA-677, an ancestral Ohlone site located near Sunol, central California in order to reconstruct their diets.

            Carbon and nitrogen isotopes from bone collagen inform on an individual’s diet within the last 5-15 years of their life (Figure 1). Carbon isotopes are often used to determine whether a diet is heavier in C3 plants (like pinon nuts) or C4 plants (like maize). However, there aren’t many C4 plants native to central California—and those that were present weren’t often consumed. Therefore, rather than using carbon isotopes to differentiate between plant consumption, we used it to differentiate between the consumption of marine (seaweed, saltwater fish, etc.) and terrestrial (acorns, deer, etc.) resources.

            Nitrogen isotopes reflect the average trophic level of the protein consumed by an individual. People who primarily consumed plants, which are found at the lowest level of the trophic system, have considerably different isotopic signatures from those who relied on resources from higher trophic levels like seals, bears, and other predators.

Figure 1
Figure 1: Carbon and nitrogen stable isotope signatures and what they indicate, courtesy of chrono.qub.ac.uk

I spent many hours in the Archaeometry Laboratory isolating collagen from the bone fragments. The process involved physically cleaning the bones, then chemically demineralizing and decontaminating them until only organic collagen remained. The collagen was solubilized and freeze-dried, then sent off to the UC Davis Stable Isotope Facility for analysis.

            After a few months, we received the results of the carbon and nitrogen stable isotope analyses (Figure 2). The carbon isotopes suggest individuals from ALA-677 consumed very little marine food, and primarily relied on terrestrial resources. The nitrogen isotopes show that individuals consumed little game relative to vegetation. There was no significant difference between male and female diets in either adult or subadult populations, which suggests few or no differences in overall dietary practices by sex. These dietary similarities are consistent with people from ALA-677 practicing “common pot” food sharing, which involves daily spoils from hunts and gathering bouts being divided equally among all members of the village.


Figure 2
Figure 2: Left: A comparison between adult male and female δ13C and δ15N at ALA-677. Right: A comparison between subadult male and female δ13C and δ15N at ALA-677.

We also assessed dietary trends over the lifetimes of individuals (Figure 3). Nitrogen isotopes show that trophic position peaks in teenagers and young adults, then decreases over time. This may represent greater hunting activity by individuals starting new families. There is little variation in carbon isotope signatures, suggesting terrestrial foods were dominant throughout individuals’ lifetimes.

Figure 3
Figure 3: Left: A comparison between age at death and δ15N at ALA-677.Right: A comparison between age at death and δ13C at ALA-677.

These results were compared to those from two nearby ancestral Ohlone sites to assess temporal variation in diet within a small region of central California (Figure 4). We sampled 27 individuals (dating 288 BCE– 503 CE) from the earliest site, Rummey Ta Kuččuwiš Tiprectak (CA-ALA-704/H), and 70 individuals (dating 1349–1839 CE) from Síi Túupentak (CA-ALA-565/H), the most recent site. Overall, individuals from ALA-677 exhibited the least amount of dietary variation, and individuals from ALA-565 exhibited the most. All individuals who resided in this area of central California relied heavily on terrestrial resources. This is not unexpected, as the ocean is over 20 km away.

Figure 4
Figure 4: A comparison between adult male and female δ13C and δ15N at ALA-565, ALA-677, and ALA- 704.

     Individuals from the earliest site, ALA-704, ate at the highest average trophic level, indicating they included a relatively high proportion of meat in their diet. While adult females from this site had slightly more varied diets than adult males, they generally consumed the same things. Similarly, at ALA-677 there is no statistically significant difference between adult male and female diets. However, these individuals were eating at a lower trophic level and were heavily reliant on terrestrial plants such as acorns, seeds, and berries. The opposite can be seen at ALA-565, where the diets of adult males and females were quite different, with males consuming a significantly higher proportion of meat.

Figure 5
Figure 5: The average trophic level of diets of males and females from each site.

These results can inform not only on an individual’s diet, but on their social environment. They allow us to understand hierarchical structures, to determine whether certain individuals or groups had preferential access to high-quality resources, and to identify cultural practices (like common pot food sharing). At ALA-677, there may have been a lack of social hierarchy—or at the very least, a lack of social behaviors which would have granted certain individuals (based on sex, status, etc.) preferential access to meat, which is considered a “high quality” resource. This is in contrast to ALA-565, where there is a clear difference in diet by sex and practices like common pot food sharing were not common practice. ALA-565 is the most recent site of the three, so it is possible that this difference may reflect the emergence of social behaviors that had not yet developed earlier in time.


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            Throughout the poster session I interacted with many people I’d cited in my undergraduate coursework. I was very nervous, as many of these people knew just as much about my topic as I did (in some cases, they definitely knew more). Although some difficult questions were asked, everyone was kind and encouraging.

            This experience allowed me to explore and solidify my interests, and inspired me to pursue a PhD in archaeology. In graduate school, I hope to use both stable isotope analyses and material sourcing with XRF to better understand hunter-gatherer diet, resource procurement, and mobility