Lithic Resource Depletion
Local sources of rock suitable for the manufacture of flaked lithic tools, such as volcanics and quartzite, are extensive and widely distributed within San Diego County. Nonetheless, it is possible that convenient or preferred material sources in particular areas may have been significantly depleted by their exploitation during the course of the prehistoric period. Distinguishing such resource depletion, if it occurred, could have important implications for correctly interpreting variation through time in assemblages of lithic tools and wastes, as well as for reconstructing the prehistoric settlement system.
Richard H. Norwood (1980) formulated the lithic depletion issue in his study of the Reading Site (SDM-W-1504) in southeast San Diego. To evaluate possible depletion, Norwood hypothesized potential diagnostic changes in the local lithic assemblage through time, including (a) a decrease in the relative frequency of desirable raw material, (b) a decrease in the size of artifacts made from desirable raw material, (c) an increase in the frequency of reused and multifunctional artifacts, (d) an increase in the degree of reduction of desirable raw materials, and (e) an increase in the relative frequency of exotic raw materials. To control for time in his study, Norwood compared assemblages that were recovered by excavation (interpreted as earlier in time) with assemblages recovered by surface collection. Norwood’s conclusions were essentially negative: most of the patterns predicted for lithic depletion were not found at the Reading Site.
Don Laylander (1991b) reexamined the question at several sites in the Spring Valley area, modifying Norwood’s methodology and his test predictions. In this study, assemblages from the upper and lower halves of the excavated deposits, rather than surface and subsurface assemblages, were compared. Test implications were formulated on the basis of a model of declining availability of nearby materials and rising procurement costs incurred in exploiting more distant material source areas. Again the results were predominantly negative, suggesting that lithic resource depletion was not an important factor in this area.
PROSPECTS
Future archaeological investigations may be able to clarify whether any significant depletion of lithic resources occurred during prehistory, either on a regional basis or at some specific source locations where there was exceptionally high-quality material or where few alternative sources were locally available. Evidence for depletion may include more intensive, material-maximizing rather than labor-minimizing use of lithic resources; increasing use of lower-quality material; and increasing use of lithic materials imported from a distance.