Abstract:
Geochemical characterization methods are commonly used in the reconstruction
of prehistoric raw material use and procurement systems. Trace element studies of lithic
source material and artifacts, specifically those made of obsidian, can reveal important
information about the environmental and cultural factors which influence the prehistoric
distribution of raw material. The current investigation uses geochemical characterization
methods and data to document and evaluate the distribution of geologic and artifact
obsidian that originates from the Silver Lake/Sycan Marsh (SL/SM) obsidian source.
This large and prehistorically significant source is located in western Lake County,
Oregon.
Few source descriptions or artifact distribution studies exist for SL/SM obsidian.
However, over the past decade, a significant increase in the use of geochemical
characterization methods has generated a wealth of data for Oregon obsidian sources.
This thesis synthesizes the results of the geochemical characterization analysis of 392
geologic obsidian specimens collected from the SL/SM source area and 1,938 SL/SM
obsidian artifacts recovered from over 200 archaeological sites in Oregon, Washington
and California. The artifact analytical data were derived from previously characterized
artifact collections compiled and archived in an extensive database. A subset of artifacts
were characterized for the purpose of this study.
Based on the results of geochemical analysis of the geologic material, two distinct
source boundaries are defined for the SL/SM geochemical source. The trace element data
show that the geologic SL/SM obsidian source material originates from two chemically-related
obsidian domes which lie in separate drainage basins. Accordingly, this
investigation establishes that the natural distribution of geologic obsidian is highly
dependent upon the regional topography.
Spatial analyses of the artifact obsidian demonstrate a widespread distribution of
SL/SM obsidian throughout central and western Oregon and parts of northwest California
and southwest Washington. Numerous cultural and environmental variables appear to
have affected the artifact distribution at local and regional levels. The findings show a
predominance of SL/SM artifact obsidian use along the western slopes of the Cascade
Range within the southern half of Oregon. Locally, use of the source appears to be less
pronounced due to the abundance of competing central and eastern Oregon obsidian
sources. The results suggest that SL/SM artifact obsidian was distributed both
intentionally and incidentally as a result of prehistoric procurement and exchange
systems.
