Prehistoric Use of the Coso Volcanic Field Amy J. Gilreath and William R. Hildebrandt No. 56 of the Contributions of the University of California Archaeological Research Facility, Berkeley

In this volume, the authors report on thirty-four prehistoric sites spanning 10,000 years in the Coso Volcanic Field.  This area is "characterized by vast deposits of naturally occurring obsidian that were extensively quarried throughout prehistory."  Both prehistoric and historic people have used the hot springs of the area.  Today, four geothermal power plants draw upon the huge underground reservoir of super-heated water and provide electricity to 240,000 urban dwellers. 201 pp., 26 figs., 87 tables, 12 maps, 1997.  $25.95.

Abstract:

Excavations at 34 sites in the Coso Volcanic Field reveal a dynamic history of obsidian use spanning at least 10,000 years. Obsidian is common and abundant throughout the area, both in primary and secondary contexts. Secondary lag deposits are widely distributed due to numerous pyroclastic eruptions that sent obsidian nodules and other debris over much of the local landscape. Primary flows, though less numerous and of more difficult access, have greater quantities of material, often forming thick bands of glass extruded from the sides of rhyolite domes. Dated primarily on the basis of obsidian hydration, analysis of over 90 chronologically discrete assemblages indicates that prior to 2800 B.P., use of the area was largely restricted to generalized, short-term exploitation of lag quarries by groups using an expansive, highly mobile subsistence-settlement system. Beginning around 2800 B.P., but reaching peak proportions between 2300-1275 B.P., a major reorganization in production strategy took place. Lag quarries were essentially ignored, and primary flows were intensively exploited, supplying obsidian to a corresponding proliferation of off-quarry biface manufacturing areas. Increases in production volume were at least partially related to long distance exchange. Contemporaneous parallel increases in Coso obsidian use among consumer populations in the Owens-Rose Valley area, southern Sierra Nevada and, more importantly, several locations in coastal southern California provide evidence of this exchange. Contrary to expectations of some, development of obsidian surpluses for exchange did not correlate with the emergence of sedentary populations and local control of the source. Rather, subsistence-settlement pattern data from surrounding areas indicate that residential mobility remained relatively high, but followed a more regularized schedule, allowing more predictable interactions among neighboring populations.

Local control of the Volcanic Field appears to have occurred for only a short period between ca. 1275-800 B.P., co-occurring with a reduction in settlement mobility region-wide. During this short period, flaked stone production became largely restricted to few primary deposits, even though obsidian consumption continued unimpeded in outlying areas. After 800 B.P., continued decreases in settlement mobility, often accompanied by higher degrees of territoriality, did not lead to an expanded inter-regional exchange system. Instead, production and exchange of Coso obsidian items essentially stopped, and the Volcanic Field was used for subsistence, largely the exploitation in unprecedented proportions of small seeds. Collapse of the Coso production-exchange system is attributed to decreased demand caused by a variety of factors including technological change and a shifting subsistence focus, while increases in territoriality may have inhibited its supply, not only by restricting direct access, but also by increasing the number of exchanges required to move material equivalent distances across the land.

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