Document Type

Thesis

Date of Degree Completion

Summer 2021

Degree Name

Master of Science (MS)

Department

Cultural and Environmental Resource Management

Committee Chair

Patrick Lubinski

Second Committee Member

Steve Hackenberger

Third Committee Member

Craig Skinner

Abstract

Within archaeological literature, a discussion of volcanic toolstones from Washington State is uncommon. Washington’s volcanic glass landscape is relatively sparse, with low-quality sources scattered within and on the east side of the Cascades, including tachylyte, obsidian, and vitrophyric obsidian. Tachylyte is a volcanic glass that forms within low-silica, basalt flows while obsidian comes from high-silica, usually rhyolitic, eruptions. Vitrophyric is a textural term used to describe an igneous rock that has a glassy groundmass with conspicuously large crystals. The low-quality and dispersed nature of these toolstones are reflected in Washington’s archaeological record by the more common occurrence of out-of-state volcanic glasses from Oregon and Idaho. The quality and abundance of these out-of-state sources has intrigued many researchers and studies but has ultimately left a gap in the literature that neglects to build a context for local, Washington State sources. After a reevaluation of x-ray fluorescence studies, 16 geochemically distinct sources were identified from Washington. This reevaluation included combination of three formerly distinct tachylyte sources (Cleman Mountain, Nasty Creek, Parke Creek) into a single source (Cleman Mountain) with five outcrop locations. An examination of the Northwest Research Obsidian Studies Laboratory database as of 2020 showed 1,663 artifacts from 260 Washington sites with sourced volcanic glass, of which only 19.3% (323 artifacts) was materials from Washington sources. Out of the 12 Washington sources identified in these artifacts, vitrophyric obsidian was the most common glass type at 42%, followed by obsidian (37%), and tachylyte (21%) which likely represents a researcher bias when sending in samples. Four of the known sources have not yet been found in any geochemically analyzed artifacts. The source analysis showed little use of tachylyte outside of a local range of the source (miles) while the appearance of Washington obsidian was more often found in sites considered non-local (>50 miles).

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