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Open Access Publications from the University of California

A Case of Heat Treatment of Lithic Materials in Aboriginal Northwestern California


The possibility thus exists that cobbles of agate and jasper were collected by Indians from the beaches and placed in fires, perhaps solely for the purpose of lithic reduction or perhaps in connection with stone boiling of water and acorn gruel (attested to by large amounts of associated fire-cracked rock of coarser variety). No careful effort was made by the Indians to control the rate at which the agate and jasper cobbles were heated and cooled, so many cobbles shattered into useless fragments. But in cases where a pot lid flake came off, the piece was plucked from the hearth, allowed to cool, and used as a core. The negative bulb scar of the pot lid flake would have provided the angular facet needed for a striking platform, thus rendering the cobble usable as a source of flakes. The pot lid flake itself was abandoned unused wherever it fell. Both the cobble and the pot lid flake would have been heat-altered during this process, as would any flakes and artifacts derived from the cobble-core.

This hypothetical lithic reduction sequence could economically explain the technological anomalies referred to earlier. It should be tested by means of by-product experiments using heat and the appropriate raw materials, and I present it here in the hope that such experiments will be tried. Such a trial-and error approach to heat treatment would have been feasible along the beaches of northwestern California, where cobbles of agate and jasper abound. If validated, this method of lithic reduction may also be found in other coastal and riverine regions in places where tough isotropic stones were being subjected to natural rounding by water movement.

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