In this study we will attempt to reconstruct interaction patterns among the Virgin Branch Anasazi of the Tuweep-Mt. Trumble region (located in Northern Arizona) with the Virgin River groups (in Southern Nevada). We will employ laboratory methods and analysis using bulk method by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). In the course of this research, we hope to derive specific chemical signatures of various ceramic artifacts and clay to identify source. From this study, we may then determine change in residential patterns, travel routes, and trade relationships.

Early ceramic analysis from the 1930's through the 1950's was primarily based on speculation, intuitive assumption, and comparison without quantification (Zedeño 1994). In the 1970's this typological method drew much skepticism as the method was rather unscientific (Bishop and Neff 1989).

Recently, more scientific applications, such as chemical analysis, have been used in provenance studies. Within the past decade, the more popular methods of chemical analysis have been through Instrumental Neutron Activation Analysis (INAA), and various forms of Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), such as Microwave Digestion (MD-ICP-MS) and Laser Ablation (LA-ICP-MS) (Speakman and Neff 2002; Kennett et al. 2002).

The Virgin Branch Anasazi inhabited the Northern Arizona, Southern Nevada, and Southeastern Utah regions (Fig. 1) between A.D. 100 and 1300 in marginal environments for both agricultural and natural resources (Larson et al. 1996; Sakai 2001).

Tuweep, located in the northwestern portion of Grand Canyon National Park, has an elevation between 1350 m and 2000 m above sea level, hot summers and mild winters with an annual precipitation slightly over 11 inches (28 cm) per year (Thompson 1970), multiple ecozones, and is geologically covered by both volcanic and sedimentary formations (Fig. 2).

The Virgin River area, in Southern Nevada, is approximately 100 km west of Tuweep and contained Anasazi sites predominately located about 450 m above sea level. The climatic conditions are characteristic of a desert environment and the area currently has an annual rainfall of four inches (10 cm) per year (Larson 1987; Larson and Michaelsen 1990). Geologically, this area is composed of sedimentary rock; thus, since olivine tempered ceramics have been found in the area, some scholars have argued that these ceramics were not produced locally but possibly in the Tuweep region (Colton 1952; Olson 1979; Lyneis et al. 1989).

Recently, interaction patterns in the Virgin River area have been studied through ceramics using INAA (Larson, Sakai, and Neff nd.). This was the first scientific study to demonstrate that olivine tempered ceramics were non-local, while red ware appeared to be a local production in the Virgin River area (Fig. 3).

To examine the origin of olivine ceramics and the evolution of interaction patterns between the Virgin River and Tuweep areas, MD-ICP-MS was conducted on 250 pot sherds and clay from both regions (Sakai 2001). This study demonstrated that olivine ceramics from both the Tuweep and Virgin River areas have the same origin, which is Tuweep (Fig. 4)

One of the questions remaining in our analysis is that the origin of the non-olivine ceramics found in Tuweep is not clear. Local clays in Tuweep do not chemically match non-olivine ceramics in Tuweep. Previous studies only included clay samples from volcanic areas in Tuweep despite the existence of both volcanic and sedimentary formations in this area.

Additional clay samples from this sedimentary formation in Tuweep were recently collected and are being incorporated here to analyze and compare non-olivine ceramics from both regions with clay from Tuweep volcanic areas and the Virgin River area to detect the trading patterns of Tuweep populations in more detail.

The beginning stages of this project involved sample collections of possible clay source material in the region and ceramic sherds (Fig. 5), which were then gathered and catalogued (Sakai pers. comm. 2003).

The categories of samples used in our analysis were: Tuweep clay found near ground level, Virgin River clay found in road cuts and drainages, Mount Trumbull clay found at least 20 cm below ground level, Tuweep ceramics borrowed from the museum at Southern Utah State College, and Virgin River ceramics from the excavation and surface collections of Dr. Daniel O. Larson (Sakai pers. comm. 2003).

• Once brought into the laboratory, the raw clay and sherds are ground into a fine powder.

• Water is added to the clay to make a small patty that is then baked in a furnace at 850 degrees Celsius for one hour to simulate the ceramic.

• The clay is then ground into a fine powder once again and it, along with the ground sherds, are placed into labeled vials.

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• 0.3g of the powdered clay and sherds are then separated for further testing and, from this point forward, all conditions of the sample are recorded.

• An internal standard of 0.5 ml (40 ppm) of Indium solution is then added to the samples for quantification control, and the samples are placed in an oven at 50 degrees Celsius overnight.

• The samples are weighed and mixed in a mixer mill for 30 minutes.

• Then they are transferred into different vials, while the weight and loss of the sample are recorded.

• Binding powder is then added to the sample bringing it to a weight of 0.5 grams.

• The samples are then pressed into pellets about 13 mm in diameter and are then ready to undergo LA-ICP-MS.

• LA-ICP-MS, a relatively new technique, is capable of multi-element characterization of many materials including glass, metal, lithics, and ceramics. Once the ceramic sample is placed into a laser chamber, a laser beam is used to ablate a small area. The ablated materials are then introduced to the ICP-MS torch to be ionized. These ions are separated based on mass and charge. They are sent to a detector which then can provide compositional data for 50-60 elements.

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The results of our research are presented below.

Validity of Method

Half of elements were found to have a correlation coefficient of more than 0.7 compared to INAA, which is currently the most dependable technique (Fig. 6). This indicates that most of the elements have a relatively good recovery rate compared to INAA data; thus, it is demonstrated that LA-ICP-MS with the "pellet method" can produce very similar results to INAA.

Data Analysis

The raw data measured by ICP-MS is subtracted and standardized by a known element (Indium), then calibrated by a known standard material (SRM612, 610, and 679) (Neff pers. comm. 2003).

The data of 83 samples with 43 elements are first converted to Log10 value and then examined by Principal Component Analysis (PCA). The scatter plot by two PCA scores, as well as several sets of each element, are created to see the tendency of grouping (Fig. 7).

Data Interpretation

All non-olivine ceramics from the Virgin River area are chemically very similar to Virgin River local clay, which is consistent with the INAA results. Tuweep non-olivine ceramics seem to have multiple origins. Though some are similar to Tuweep local clay indicating they are a local production, other ceramics were found to be similar neither to Virgin River nor Tuweep clay, inferring the existence of another trade group outside the Virgin River area. The Tuweep red ware was found to be chemically similar to Virgin River red ware and local clay. This may indicate that Tuweep red ware might have been brought from the Virgin River area.

Although our research is still in progress, the significance of our studies is that we were able to find patterns of ceramic movement that will help us further in our provenance studies confirming that bulk method LA-ICP-MS is an excellent research tool.

In addition, the research results indicate possible additional trading patterns associated with the Tuweep population center. This provides us with a deeper insight into interaction patterns of the Virgin Branch Anasazi.

First and foremost I would like to thank Sachiko Sakai for teaching me these methods and having patience with me. Dr. Daniel O. Larson and Dr. Elizabeth Ambos, thank you for being such incredible mentors. Dr. Hector Neff, thank you for your knowledge and wisdom in this project. Mr. Keith Miller of Lakewood High School and Michael Cruz, thank you for all your support; and to my fellow GDEP students, Anne Breister and Marlene Cortez, thanks for the great moments spent together. Another thanks to Crisanne Hazen, those involved with GDEP, Dr. Laurel Breece of Long Beach City College, and the National Science Foundation grant #geo-0119891 for giving me this incredible opportunity. Lastly, thanks to James Balestrery and my family for supporting me throughout this endeavor.

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