Lithic Quarrying
Lithic raw materials were initially acquired prehistorically at locations that have been designated as quarries. Because of the high visibility of lithic artifacts within the archaeological record, an important part of interpreting that record is to understand the manner of acquisition, the social context, and the specific objectives involved in lithic material collection. Jonathon E. Ericson (1984:8) observed that “if we are to advance our understanding of regional patterns of procurement, exchange, and technology, we must know what events have occurred at the quarries.”
In San Diego County, quarrying took place primarily in areas in which suitable rock was exposed at the surface, either as large cobbles or in bedrock outcrops, rather than in excavated mines. The most abundantly quarried material was probably metavolcanic rock from the Santiago Peak Formation of the western foothills, although many other rock types were also exploited.
A range of questions relating to quarry exploitation can be posed:
- How was quarry use organized? Were quarries exploited regularly by the same individuals or by small groups of locally-based “owners,” or were they visited casually and irregularly by people from throughout a wide region? One way to address this question may be to consider the form in which the resource was removed from the quarry. It might be suggested that locally based exploiters would have been more likely to remove the lithic material from the quarry at an early stage in the reduction sequence, for finishing at a nearby habitation base, whereas casual users would have been more likely to complete more of the finishing work at the quarry site. However, John R. Cook (1985) hypothesized that locally based quarriers at Rancho Cielo completed much of the reduction at the quarry, whereas users of the same resource who came from farther away removed quarried material to separate workshops in the vicinity. In a GIS analysis of recorded sites in the Jacumba/McCain Valley region, 41 sites containing lithic quarries were identified (Laylander et al. 2015). While 28 of these sites were typed as quarry/workshop sites, 13 were assigned to other site types, including habitation bases (n = 3), temporary camps (n = 4), biotic resource extraction/processing sites (n = 3), and artifact scatters (n = 3). Another clue might come from examining the hammerstones that were left at the quarry site. At quarries, a small group of regular users would probably have continued to use hammers that were brought to the site until the hammers had become unusable through breakage; on the other hand, casual users of the quarry might have abandoned larger numbers of lightly used and still-functional hammers. The problem of the organization of quarry use can also be approached from the perspective of regional consumption patterns. Andrew R. Pigniolo (1992) suggested, following Colin Renfrew (1977), that regional patterns in the frequency and form of discarded lithic material from a known quarry source might provide a basis for differentiating exploitation by direct procurement from redistribution through exchange.
- On what basis was material from within a particular geological formation selected for exploitation? Plausible selection criteria include the grain size of the rock’s groundmass, the abundance and size of phenocrysts within porphyries, the abundance and size of vesicles, the extent and orientation of natural fracturing, the extent of weathering within natural fractures, the size of the available nodules, and the color of the rock. Color preferences might have been based in ideology or aesthetics, or perhaps used as an indicator of the physical properties of the rock, such as hardness, related to its mineralogical composition. The selection criteria that were applied may be isolated through comparison of the different materials that were available at the quarry and that were variously left untouched, abandoned after initial testing, or fully exploited.
- What were the desired end-products of the lithic production that was begun at the quarry? For instance, was the material being used for projectile points, bifaces, scrapers, hammer/choppers, or groundstone tools? The success with which the end-products can be discerned at quarry sites may depend upon how much of the reduction process was carried out there. If only cores or crude blanks were being prepared and removed, the objectives may not be recognizable, but if tools were being finished, then nearly-finished discards and diagnostic debitage may be present. Changes through time in the desired end-products might be reflected by differential patination on the flake scars of material that had been discarded as unusable during one period and was worked again during a later period.
- What were the specific reduction techniques favored for particular materials and during particular time periods? How prevalent were anvil, bipolar, hard hammer, soft hammer, and prepared platform techniques at the quarries? Was fire used in extracting material from outcrops or to heat-treat quarried material to improve its flaking properties? Detailed analyses of quarry features, hammerstones, anvils, cores, and debitage may be able to answer these questions.
- What was the scale of lithic procurement operations over the course of a quarry’s life span? Clay A. Singer and Ericson (1977) suggested a manner in which the total output of a quarry might be estimated from the archaeological residues, given recognized end-products plus the use of replicative experiments to determine the typical quantity of residues produced in their manufacture.
PROSPECTS
Future archaeological investigations may be able to identify the ways in which quarry use was organized and the objectives for which specific quarries were exploited. Replicative experiments may be able to clarify the suitability of various materials and techniques, along with their diagnostic traces in the archaeological record. Relevant archaeological evidence may include the characteristics of quarry materials that were not exploited or that were tested but rejected, as well as the waste products from tool making and discarded processing tools such as hammerstones. Other evidence may be obtained from spatial patterning in the distributions of quarries, lithic workshops, and habitation sites, and from the frequency distributions of specific materials in archaeological sites as a function of their distance from the source quarry.
| Quarry Location | Rock Type | Form | References |
| Bankhead Springs | quartz | outcrop | Smith 1980 |
| Escondido | volcanic rock | cobble, outcrop | Berryman 1980; Vaughan 1982 |
| Mount Laguna | aplite, steatite | outcrop (aplite), boulder (steatite) | Graham 1981 |
| Otay Mesa | volcanic rock | cobble | Rosen 1990 |
| Piedra de Lumbre Canyon | cryptocrystalline silica | outcrop | Pigniolo 1992 |
| Ramona | volcanic rock | outcrop | Smith 1979 |
| San Dieguito River | volcanic rock | outcrop, cobble | Cook 1985 |
| Table Mountain | volcanic rock | cobble | May 1987 |