Wednesday, February 13, 2019

90th Anniversary Blog Series: Artifact 4

In 2019, Pueblo Grande Museum (PGM) will be observing our 90th anniversary as an institution. As part of our celebration, we’re featuring interesting research happening at PGM. 
One of our largest research projects is the fifth volume of the Pueblo Grande Archival Project Series (Archival Series). The project began in 1989 with the goal of creating an archaeological report for the unpublished excavations conducted within the boundaries of Pueblo Grande Museum and Archaeological Park. These excavations began in 1929 and continued into the 1980s. Before the Archival Series, the results of more than 50 years of work had never been published or reported. To date, three volumes have been published.

The fifth volume of the Archival Series will focus on objects excavated from the site, and the documentation is being conducted by professional archaeologists who are volunteering their time. We’ve asked each archaeologist to select the most interesting object they’ve analyzed for a blog series leading into our 90th year as Pueblo Grande Museum!
Our fourth featured blog is by Volume 5 researchers Craig M. Fertelmes PhD. of Logan Simpson, Inc. and Michael Stubing of Jacobs Engineering, Inc.

Ground Stone Analysis For the Pueblo Grande Archival Project Series:

As part of on-going research for the fifth volume of the Pueblo Grande Museum (PGM) Archival Project Series, analysis of the utilitarian ground stone (manos, metates, mortars, and pestles) was conducted. The purpose of the ground stone analysis was to provide a descriptive summary of previously unreported artifacts from PGM, and to help answer research questions specific to both the ground stone collection and to the overall archival project. While many noteworthy results have come to light from the analysis, one of the more interesting aspects is learning where the material to make the manos, metates, and other ground stone artifacts found at PGM originally came from.

With the help of portable X-ray fluorescence (PXRF) technology, archaeologists are now able to determine the source locations of many material types, including the lithic resources used to make ground stone. The PXRF technology uses sophisticated hardware to measure geochemical attributes in rocks (and other materials) in a non-destructive fashion. By matching the geochemical signatures in the analyzed artifacts with samples from source areas in the region, archaeologists can pinpoint the locations that served as ground stone quarries.

As part of the PGM analysis, 50 vesicular basalt (an igneous rock prized for its suitability as ground stone) artifacts were subjected to PXRF analysis. The artifacts consisted of 29 manos and 21 metates. The PXRF analysis found that three source locations accounted for the vast majority of ground stone artifacts in the sample: the Middle Gila River Valley, the New River region, and the McDowell Mountains each accounted for approximately one-third of the total sample.

Interestingly, these three primary source locations are situated at roughly the same distance from PGM. The Middle Gila River Valley includes the San Tan Mountains, which are located approximately 40-45 km (25-28 mi.) southeast of PGM. The New River source region consists of several low mountains including Adobe Mountain, the Deem Hills, Hedgpeth Hills, and West Wing Mountain; this area is approximately 30-40 km (19-25 mi.) northwest of PGM. The McDowell Mountains are northeast of PGM, approximately 24-28 km (15-18 mi.) away.

The above areas have been previously documented as important ground stone raw material sources for the Hohokam, and the results of the PXRF study will help to solidify these designations. However, it is interesting to note that residents of Pueblo Grande made use of multiple sources located roughly the same distance from the site, rather than relying on a single location. Whether this was due to trade conditions, production/control systems in place at the time, a preference for lithic characteristics from each source, or other reasons is still unknown; however, the ground stone analysis of the PGM collection has helped to identify which sources were utilized the most.


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