Description

Petrology of Sand and Rock Samples from the Gila Butte-Santan Mountains Area, Central Arizona (TR1995-7) (PDF)

Micaceous tempering materials included in prehistoric ceramics thought to have been produced at Gila Butte and the Santan Mountains were widely distributed in Central Arizona during the Colonial and Sedentary Periods, and were present from Early Ceramic times. However, no comprehensive study on the composition of source materials available in this area has ever been conducted.

On March 4 and 5, 1994, Elizabeth Miksa of Desert Archaeology, Inc., David Abbott, an independent contractor, and Jerry Howard, of the Mesa Grande Museum, collected a total of 47 geologic samples (31 sand and 16 rock) from Gila Butte and the Santan Mountains on land owned by the Gila River Indian Community (Figure B.1). Collection was made with the permission of the Community, and under the supervision of a Tribal Ranger.

The sand and rock samples were collected to provide material for petrographic characterization of the sand and rock types available on Gila Butte and in the Santan Mountains. Up until now, only limited samples have been available from this area to compare to sand and rock tempers thought to originate at Gila Butte or in the Santan Mountains. Our first goal, therefore, was to identify the range of tempering materials available in this area. An additional goal of this research has been to locate and identify, if possible, any of the fine-grained red rock fragments seen in some sherds tempered with coarse-grained muscovite-schist-rich material. These rock fragments have been identified by Diana Kamilli (Appendix A) as being a sedimentary rock, probably a siltstone (Kamilli 1993).

The analytical techniques chosen for this project are petrographic modal analysis, or point counting, and qualitative hand sample description. Point counting provides quantitative information on the volume of each type of rock or mineral in the point-counted sample. These data are suitable for statistical analysis. Qualitative hand sample description provides data on how the samples look in hand sample so that they can be recognized when they occur as sand temper in sherds. None of the petrographic projects conducted by the author prior to this one have included point counts of rocks as part of the analysis. However, because of the archaeological importance of the schist temper thought to originate in this area, rocks as well as sands were included in the point count analysis.