Prehistoric habitation sites with shell midden deposits containing quantities of red abalone shells, which I call red abalone middens, exist on Santa Cruz, Santa Rosa, and San Miguel Islands. They are also found on some of the southern Channel Islands, particularly San Nicolas Island. Although red abalone middens contain shells from other mollusk species, particularly California Mussel (Mytilus californianus),they are distinctive in that they contain many whole and fragmentary red abalone shells, whereas most other sites on the islands generally contain relatively few abalone shells, and those abalone shells present usually are of black abalone (Haliotis cracherodii),a smaller species.
In the 1950s, the noted oceanographer, Carl L. Hubbs, visited the northwestern coast of Santa Rosa Island, where he saw archaeological sites being investigated by Phil C. Orr of the Santa Barbara Museum of Natural History. Several of these sites, determined to have been occupied between about 5500 and 6000 BC on the basis of radiocarbon dating, contained significant quantities of red abalone shells, and Hubbs argued that their prevalence in these sites was indicative of sea water temperatures significantly cooler than present at the time of occupation. Furthermore, Hubbs reasoned that sites dating later in time, containing black abalone shells, would have been occupied at times when sea water temperatures were close to those prevailing today.
Hubbs's argument was based in part on the current distribution of red abalone along the California coast. Today, red abalone is mainly a subtidal species in the Santa Barbara Channel, whereas black abalone is intertidal. North of Santa Barbara County, however, red and black abalone both occupy the intertidal zone, with red abalone usually occurring lower in the intertidal zone than black abalone. North of San Francisco, red abalone historically has been the dominant species in the intertidal zone. This gradual northward shift in the proportions of red and black abalone species in the intertidal zone correlates with decreasing sea water temperatures as one moves up the California coast. Hubbs recognized that red abalone preferred colder waters than black abalone, and he assumed that red abalone would be prevalent in the intertidal zones around the Channel Islands only if sea water temperatures were as cool as they were several hundred miles up the California coast, where red abalone lives in the intertidal zone. Of course, Hubbs also assumed that the prehistoric occupants of the Channel Islands would collect abalone from the intertidal zone and generally would not have bothered to dive for them in deeper waters.
In the early 1980s, one of UCSB's graduate students, Larry Wilcoxon, encountered in a test pit a dense layer of red abalone and mussel shells within a matrix of dune sand at a site near the western extreme of Santa Cruz Island (the site is designated SCRI-333). When he encountered this layer, he had already excavated through dense archaeological deposits extending from the ground surface to more than a meter below surface. We suspected the red abalone midden dated to the same time as those Orr had investigated on Santa Rosa Island. As it turned out, radiocarbon dates indicated that the red abalone midden dated around 3350-3800 BC, or almost two thousand years later.
The red abalone midden at SCRI-333 inspired me to locate others on Santa Cruz Island and to obtain radiocarbon dates from them. Larry Wilcoxon had located a few at the heads of arroyos near the western end of the island, and my colleague Chester King, who had carried out a reconnaissance several years earlier along the southern shoreline near the western end of the island, reported that he had seen others. In 1984 I retraced King's and Wilcoxon's reconnaissances and recorded seven sites with red abalone middens. I obtained radiocarbon dates for six of these sites, and I re-examined records of sites for which I had obtained radiocarbon dates in 1974-1975 to determine whether any of these contained noticeable quantities of red abalone shells. I found that three did, so the total number of Santa Cruz Island sites containing red abalone middens in the mid-1980s was ten. All except two of these ranged in age between 4500 and 2800 BC; one of the exceptions dated to about 5500 BC and the other to about 2000 BC.
In summary, most of the dates from Santa Cruz Island red abalone midden sites indicate that there was a discrete period of time centering around 3700 BC when inhabitants of the island ranged along the coastline and collected significant quantities of red abalone along with other shellfish and consumed their meat. Only one of the red abalone middens appeared to fall within the range of time of the Santa Rosa Island red abalone middens, and another appeared to be anomalously young.
Having determined that the dates of occupation of most of red abalone middens on Santa Cruz Island clustered within an interval of time about 1700 years long, I wondered whether sea water temperatures indeed were significantly cooler, as Hubbs had argued some 25 years earlier. If so, air temperatures also would have been cooler, implying that both marine and terrestrial environments may have differed in significant ways from the conditions prevailing today. My colleagues James Kennett and Douglas Kennett and I decided to test Hubbs's proposition through measurement of the proportion of oxygen-18 isotope in the carbonate comprising the shells in these middens. The analysis was based on the fact that the amount of oxygen-18 incorporated into the shell while the shellfish is alive and growing is determined in large part by water temperature. To measure the amount of oxygen-18, small samples of powdered shell were analyzed by a mass spectrometer in James Kennett's laboratory. Instead of obtaining the samples from abalone shells, we used California mussel shells, which was the species used in other oxygen-18 analyses. The analysis revealed that sea water temperatures were about 2.5°C cooler 3350-3800 BC than today. As Hubbs had argued, the prevalence of red abalone shells in a midden may be used as an indicator of significantly cooler water temperatures at the time the abalone were collected.
This prior research and the growing number of red abalone middens on the Channel Islands that have been dated by my colleagues and me to the period prior to 2800 BC has provoked a number of questions regarding the context of these sites in prehistoric cultural systems and the evolution of cultural complexity. These questions also have grown out of current studies of prehistoric hunter-gatherers in different parts of the world, particularly those who lived in coastal settings. Those questions guiding my long-term research are:
Was there a significant increase in island population beginning around 4500 BC, and if so, was it linked to an environmental shift that made some or most food resources more abundant? Specifically, did a shift to cooler ocean waters increase the productivity of marine foods?
How abrupt was the population increase, if it occurred?
Where population numbers on the islands between about 5500 and 6000 BC higher than during the succeeding thousand years? In other words, was there a period of very low population between 5500 and 4500 BC, and if so, was population depressed because of environmental conditions that diminished the abundance of food resources?
What kinds of subsistence activities did the inhabitants of the sites undertake aside from collecting and consuming shellfish? In particular, how important were other marine foods such as fish and sea mammals?
How did they acquire these other marine foods? That is, what was the nature of the technology used in food acquisition, and were boats critical to their maritime subsistence activities?
Is there evidence for changes in emphasis on certain food resources through the period from roughly 6000 to 3800 BC; specifically, is there evidence of subsistence intensification? If so, did any of these changes entail increasing dependence on marine fish and mammals? Were any of these changes associated with adoption of more sophisticated technology for acquiring or processing food resources, such as more reliable watercraft or more elaborate fishing gear?
Alternatively, were changes in subsistence a product of certain environmental changes that made some food resources more or less abundant than before, or did various social factors favor changes in food procurement and processing activities?
How different were cultural systems during the period of apparently low population numbers in comparison to those before 5500 and after 4500 BC?
Did the people inhabiting these sites live only at or very near the coast, or did they also occupy sites in the interior of the island? If interior as well as coastal sites were occupied, what was the season or seasons of occupation at the coast and in the interior?
I realized at the beginning of the RAMP that very little information was available from red abalone middens to know how to address these questions. Chronological information still was scanty, and I had only a gross idea of the nature of site contents. I felt that the chances were good that I could identify some aspects of subsistence change, and I was confident that I could construct a much more detailed chronological framework. I viewed the project as a first substantial step in a long-term research program for addressing-and refining-these research questions.
References
Glassow, Michael A., 1993. The Occurrence of Red Abalone Shells in Northern Channel Island Archaeological Middens. In Third California Island Symposium, Recent Advances in Research on the California Islands,edited by F. G. Hochberg, pp. 567-576. Santa Barbara Museum of Natural History, Santa Barbara.
Glassow, Michael A., Douglas J. Kennett, James P. Kennett, and Larry R. Wilcoxon, 1994. Confirmation of Middle Holocene Ocean Cooling Inferred from Stable Isotopic Analysis of Prehistoric Shells from Santa Cruz Island, California. In The Fourth California Islands Symposium: Update on the Status of Resources,edited by W. L. Halvorson and G. J. Maender, pp. 223-232. Santa Barbara Museum of Natural History, Santa Barbara.
Hubbs, Carl L., 1967. A Discussion of the Geochronology and Archaeology of the California Islands. In Proceedings of the Symposium on the Biology of the California Islands,edited by R. N. Philbrick, pp. 337-341. Santa Barbara Botanic Garden, Santa Barbara.
Orr, Phil C., 1968. Prehistory of Santa Rosa Island.Santa Barbara Museum of Natural History, Santa Barbara.