Title
From the Desert to the Coast: Trade and Travel Among Prehistoric Inhabitants of San Diego County
Author

Monica Steckling
American River College, Geography 350: Data Acquisition in GIS; Spring 2008
Contact Information (Address, phone, email: Optional)
Abstract

The purpose of this paper was to identify trade and travel patterns among the prehistoric inhabitants of San Diego County through the use of petrographic and GIS analyses.
Introduction

Pottery analysis is valuable in the interpretation of cultural resource sites, as it provides data on the preferred clay sources and trade and travel pattern of prehistoric Native Americans. Typically, when pottery sherds are recovered from an archaeological site in the San Diego County region, they are found in small quantities. Moreover, the collection usually consists of small, fragmented body sherds and a few rim sherds. Without diagnostic pieces (incised, decorated, etc.) or whole vessels, analysis of vessel attributes, vessel morphology, and specific activities cannot be addressed. In a situation where few pottery sherds are present to examine, a different type of analysis may be more useful. Petrographic analysis of sherds allows the researcher to identify mineral inclusions of the sherds that are specific to geologic zones, providing data on the possible trade and movement of the people who once occupied a given site. For large pottery collections, petrographic analysis is also helpful, as it provides information on local clay source preferences. In the San Diego County region, pottery artifacts are created from local clays in the mountains or from clays farther east from different areas of the desert. To differentiate which clays are local and non-local, clays need to be identified in relationship to their geological source. The different geologic zones that make up the San Diego County region include the coastal plains, the Peninsular Range Mountains, and the Salton Trough desert. The coast and desert regions contain alluvial clays derived from marine and lacustrine sedimentary rock, while the Peninsular Range Mountains contain residual clays derived from gabbroic-granitic materials. An analysis of the mineral composition of the pottery sherd must be conducted in order to identify the geological source from which the clay was obtained. The type of pottery ware can be identified, once the geological source of the clay has been determined. Once the geologic sources of the clays have been identified, GIS was used to georeference the locations from where the pottery sherds were collected from and to identify the trade and travel patterns of the prehistoric occupants. Map data for the pottery sherd locations was acquired in the field during excavation using GPS units and base map data was acquired through the author’s employer. The results of this analysis were used to identify patterns of prehistoric trade and travel, which is an important archaeological research issue. The presence of Native American trails and trade activities among different cultural groups in the southern California regions was noted by early travelers and ethnographers. The procurement of non-local clay resources would identify contact with other cultural groups outside of the coastal San Diego region.
Background

In the San Diego region, prehistoric potterys are created from local clays in the mountains or from clays farther east from different areas of the desert. To differentiate which clays are local and non-local, clays need to be identified in relationship to their geological source. The different geologic zones that make up the San Diego region include the coastal plains, the Peninsular Range Mountains, and the Salton Trough desert. The coast and desert regions contain alluvial clays derived from marine and lacustrine sedimentary rock, while the Peninsular Range Mountains contain residual clays derived from gabbroic-granitic materials. Three types (Tizon Brown Ware, Salton Brown Ware, and Colorado Buff Ware) of pottery wares are typically identified at archaeological sites within the San Diego region. Most commonly found are Tizon Brown Ware pottery, as these types of wares are produced from local clay sources. Salton Brown Ware and Lower Colorado Buff Ware pottery are often present in much smaller quantities, as these wares are produced from non-local clay sources. The following section provides a brief description of the three common pottery wares in the San Diego County region. Tizon Brown Ware Previous attempts to produce pottery ware typologies for San Diego County has resulted in the identification of two different ware types: brown ware and buff ware (Rogers 1936:4). Brown wares, referred to as Tizon Brown Wares, are frequently associated with the mountain region. Tizon Brown Ware is the most common ware in San Diego County. The term Tizon Brown Ware was originally associated with the northwestern Arizona region, and many Southern California potterys were later included under this name (Euler 1959). As a result, there has been a tendency to classify Southern California potterys under the all-inclusive Tizon Brown Ware type, without any subtypes. Although this classification suggests some regional continuity between Arizona and Southern California pottery, this is not the case. Problems arise with this classification because many variations of Tizon Brown Ware have been recovered in Southern California. Moreover, many brown ware sherds are not restricted to mountain sites and can be found along the coast and inland near the Salton Sea (Van Camp 1979:47). Tizon Brown Ware vessels were made from residual granitic-derived clays. Residual clays are found primarily in the mountain and coastal areas of San Diego County. These clays are the end products of weathering and breakup of gabbroic and granitic outcroppings of the Peninsular Range Batholith. Along the western side of the Peninsular Range, gabbroic rocks predominate and are characterized by a high concentration of plagioclase and amphibole. Along the eastern side, which slopes and extends into the desert region, granitic rocks predominate. Consequently, there is an noticeable decline in the amount of amphibole in the granitic rocks (eastern side), but a greater concentration of mica (biotite and muscovite) and quartz (Hildebrand et al. 2002). In contrast, clays from the eastern, granitic side have few or no amphibole minerals (Hildebrand et al. 2002). The clays contained in Tizon Brown Ware originate along the western, gabbroic side of the Peninsular Range and thus contain inclusions of plagioclase, quartz, mica, and amphibole. Lower Colorado Buff Ware The other common type of pottery found in Southern California is buff ware. Buff ware pottery is often referred to as desert wares, and are also known as Lower Colorado Buff Wares. Buff wares are made from sedimentary clays that result from the mixture of soil and water. Coarse particles are left behind, while fine particles are deposited some distance from the parent source. Sedimentary clays are finer in texture and have a more homogenous composition when compared to mountain clays (Rice 1987:37). These clay types can be found in former lake bottoms and alluvial deposits in the Colorado Desert and in Imperial County, near the ancient Lake Cahuilla. The minerals contained in Lower Colorado Buff Ware include quartz, feldspar, rare instances of amphibole, and sometimes mica. Salton Brown Ware Salton Brown Ware is another desert ware, similar in appearance to Tizon Brown Ware. Lower Colorado Buff Ware is easily discernible from the two types of brown ware. However, distinguishing Salton Brown Ware and Tizon Brown Ware is not as straightforward. These two brown wares cannot be differentiated based on visual inspection alone because their exteriors are so alike. One of the main factors that distinguish a Salton Brown Ware from a Tizon Brown Ware is the absence of the amphibole, a rock-forming mineral that weathers into clay (Rice 1987:34). Salton Brown Ware originates along the eastern side of the Peninsular Range (western Salton Trough sediments) and has a higher content of mica, quartz, and a rare amphibole when compared to Tizon Brown Ware (Table 1).
Table1.jpg
Methods

In Hildebrand et al.’s (2002) study both trace- element (NAA) and petrographic thin-section analyses were used to examine a representative sample of pottery sherds for southern San Diego County. Salton Brown Ware sherds had an average mineral composition of 61% quartz, 11% plagioclase, 15% biotite, 6% muscovite, and 4% amphibole (see Table 1) (Hildebrand et al. 2002). Analysis of the Tizon Brown Ware sherds indicated an average mineral composition of 51% quartz, 20% plagioclase, 4% biotite, 1% muscovite, and 20% amphibole (see Table 1) (Hildebrand et al. 2002). These results suggest that Salton Brown Ware has a higher percentage of quartz and mica and almost no amphibole, while Tizon Brown Ware has a higher percentage of amphibole and plagioclase. Petrographic Analysis Methods A total of 326 pottery sherds were excavated from site CA-SDI-8303. The sherds were first placed into different sample groups based upon mica (biotite and muscovite) concentration, sherd thickness, rim shape variability, surface color, and core color. Sherds with recent broken edges were checked to see if they mended with other sherds within the sample group. Both procedures reduced the possibility of analyzing sherds from the same parent vessel. As a result, five different sample groups were identified. After all the sherds had been placed into different sample groups, each group was placed into plastic bags and a random sherd was selected as the representative sample for each group. The sherds were submitted to the San Diego Petrographics Laboratory for the creation of thin-section samples. Each sherd was enveloped in epoxy resin, then polished and cemented to a glass slide. The sample was then cut and polished to a thickness of 30 microns, and finally sealed with a glass-cover slip. Once the thin-section samples were returned to the laboratory, they were examined under a polarizing (petrographic) microscope by transmitted light (plane-polar and cross-polar) from 28X to 1500X magnifications. Important mineral characteristics that we considered when examining the thin sections included distinctive cleavage, twinning, alteration, zoning, exsolution, or the presence of inclusions. The mineral inclusions were identified using the point-count method, with a minimum count of 100. Each slide was examined once under the polarizing microscope using the point count method and then a second time examining the entire slide for a general observation of the mineral composition. GIS Mapping Methods The author received datasets from her employer, which were used to create a base map in ArcMap of San Diego County. The map was projected in NAD 83 and then an archaeological site shapefile was added to the base map. Data for the archaeological sites was obtained in the field during excavation and survey of the sites. GPS points of artifact locations and excavated units were collected and once the data had been uploaded into ArcMap, site boundaries in the form of polygons and points were created. Afterwards, a geologic layer of San Diego County was added. USGS maps and specific location data were not used as the actual locations for the archaeological sites are not for public review.
Results
A total of 326 pottery sherds were recovered during the excavation of site CA-SDI-8303. Results of this analysis indicate that 97% (n = 319) of the sherds recovered from site CA-SDI-8303 are Tizon Brown Ware, 1% (n = 2) are Colorado Buff Ware, and 2% (n = 5) are Salton Buff Ware.

Analysis
The results of the pottery analysis for site CA-SDI-8303 provided data on the geologic location of clay sources that were used to manufacture pottery. The presence of the Lower Colorado Buff Ware indicates that trade and/or travel occurred to the former lake bottoms and alluvial deposits in the Colorado Desert and in Imperial County, near ancient Lake Cahuilla. The presence of Salton Brown Ware suggests that trade and/or travel occurred to the eastern side of the Peninsular Range (western Salton Trough). Although Tizon Brown Ware are considered local wares throughout the San Diego region, the clay sources are still approximately 10-20 miles east of site CA-SDI-8303 and some degree of travel and/or trade was necessary to obtain and/or manufacture these pots. These results provide important clues about the prehistoric inhabitants of site CA-SDI-8303. Hildebrand et al.’s (2002) study on coastal and mountain sites indicates a pattern of westward transport of Lower Colorado Buff Ware and Salton Brown Ware into the Peninsular Range and coastal regions. There was little evidence for eastward transport of pottery from the coast to the Peninsular Range, or from the Peninsular Range to the desert. Ethnographic information indicates that the Luiseño Indians of San Diego traveled on a seasonal basis, migrating in the late summer and fall to foothill and mountain sites then traveling to sites near the coast during winter and spring (Bean and Shipek 1978). Such movement would provide the setting for procurement of non-local clay as well as trade for non-local wares. Trade may also have functioned as a reaffirmation of social ties, especially regarding hunting and gathering territories, migration, allies, quarrying, and religious-ceremonial functions. As CA-SDI-8303 is located near the coast and it is likely that the desert wares (Salton Brown Ware and Lower Colorado Buff Ware) were traded into the area. Pottery vessels can be efficiently carried long distances through the use of grass, carrying bags and nets as long as they are not too heavy and they have restricted vessel openings as to not allow the contents to spill out (Arnold 1985; Rice 1987). Traded pottery vessels would also served the purpose of transporting traded grains, seeds, nuts and other dry goods (Rice 1987). Five additional northern San Diego County coastal sites (CA-SDI-8694, CA-SDI-8797, CA-SDI-9097, CA-SDI-12262, CA-SDI-14784) were examined as part of the study. Site CA-SDI-9097 is located approximately one-half mile north of site CA-SDI-8303, while sites CA-SDI-8694 and CA-SDI-8797 are located on hills adjacent to site CA-SDI-8303. Sites CA-SDI-12262 and CA-SDI-14784 are located approximately 5 miles north of sites CA-SDI-8303 and CA-SDI-8694. Petrographic analysis was conducted on pottery sherds recovered from previous excavations at these five sites (Gallegos et al. 2000, 2001) (Table 2). The thin section samples and results for sites CA-SDI-12262 and CA-SDI-14784 were combined to represent one site location as they are located adjacent to each other. Seventy percent (n = 177) of the pottery recovered from site CA-SDI-8694 were identified as Tizon Brown Ware, 25% (n = 63) were identified as Salton Brown Ware, and 5% (n = 12) were identified as Lower Colorado Buff Ware. At site CA-SDI-8797, 100% (n = 49) of the pottery recovered were identified as Tizon Brown Ware. Eighty-five percent (n = 44) of the pottery recovered from site CA-SDI-9097 were identified as Tizon Brown Ware and 15% (n = 8) were identified as Lower Colorado Buff Ware. At sites CA-SDI-12262 and CA-SDI-14784, 84% (n = 54) of the pottery were identified as Tizon Brown Ware, while 16% (n = 10) were identified as Salton Brown Ware. In addition to site CA-SDI-8303, these five additional sites (CA-SDI-8694, CA-SDI-8797, CA-SDI-9097, CA-SDI-12262, CA-SDI-14784) demonstrate a pattern of westward transport of Lower Colorado Buff Ware and Salton Brown Ware into the Peninsular Range and coastal regions (see Figure 1).
Table2_finalproject.jpg
Figure 1
Figure 1
Conclusions
Through the use of petrographic analysis and GIS analysis, the results of the current study identified a prehistoric pattern of westward trade and/or travel from the desert and mountains to the coast. Additional pottery analysis data from northern San Diego County sites is required to understand the role of the desert region in regards to the foothill/mountain - coastal migration pattern. The ethnographic literature states that the Luiseño traveled on a seasonal basis, migrating to and from the foothill and mountains to the coast, however little is known about travel east of the foothills and mountains. Contact through trade and/or travel was occurring with desert groups, as is evident with the presence of desert wares at the five sites, yet there is a paucity in the ethnographic literature on such trade or travel ties. Moreover, supplementary data is necessary on artifact assemblages from northern San Diego County mountain sites. Mountain sites are considered to be the cultural transition area between the coast/inland and the desert regions. Such mountain sites tend to have increased artifact type variability that is rarely seen at sites located further west. Research on mountain sites (i.e., Palomar Mountain) east of the current project area has not been as extensive and thus, leaves a major gap in the archaeological record. Furthermore, without research on trade and travel ties with eastern sites, to some degree, archaeologists lack a truly accurate understanding of trade and travel issues in northern San Diego County.


References
Arnold, Dean E. 1985 Ceramic Theory and Cultural Process. Cambridge University Press, Cambridge.


Bean, Lowell John and Florence C. Shipek 1978 Luiseño. In Handbook of North American Indians, Volume 8. Ed., Robert F. Heizer. Pp. 550-563.


Euler, R. 1959 Comparative Comments on California Pottery. Archaeological Resources of Borrego State Park, edited by C. W. Meighan, pp. 41-44. University of California Archaeological Survey, Annual Report, 1959:25-44. Los Angeles.


Gallegos, Dennis, Tracy Stropes, Richard Cerreto, Nina Harris and Larry Tift 2000 The Eternal Hills Project: Cultural Resource Survey and Test Program, City of Oceanside, California. Ms. on file at Gallegos & Associates.


Gallegos, Dennis, Tracy Stropes and Monica Steckling 2001 Cultural Resource Test Program for the Wilson Property, Carlsbad, California. Ms. on file at Gallegos & Associates.


Rice, Prudence M. 1987 Pottery Analysis: A Sourcebook. University of Chicago Press Chicago, Illinois.


Rogers, Malcolm 1936 Yuman Pottery Making. San Diego Museum Papers, No. 2. San Diego, California.


Van Camp, Gena R. 1979 Kumeyaay Pottery: Paddle-and-Anvil Techniques of Southern California. Ballena Press, New Mexico.