Obsidian Scavenging
Reuse of obsidian is recognized by the presence, on different flaked surfaces of a single tool or piece of debitage, of two or more different hydration readings (differing by a minimum of 0.4 microns, to exclude differences that might reflect normal reading error). Scavenging and reuse were discussed by Elizabeth Skinner (1988) and by Sharon A. Waechter and Thomas M. Origer (1993) for northern California prehistoric sites. In those studies, it was suggested that discarded obsidian was an important resource under some circumstances and that patterns in the frequency of scavenging may illuminate such matters as ethnic boundaries, settlement patterns, and changes in technology. Understanding patterns of scavenging may also be important in interpreting the chronological implications of hydration readings.
Waechter and Origer briefly surveyed the obsidian literature on a statewide basis for the frequency of multiple hydration bands. From 22 sites in the South Coast area (San Diego, Orange, Los Angeles, Ventura, and Santa Barbara counties), 16 out of 435 specimens, or 3.7%, had multiple bands. This frequency put the South Coast behind the North Coast Ranges (8.9% of the specimens with multiple bands) and Mono/Inyo Counties (8.0%) but ahead of Desert (2.7%), South-Central Sierra Nevada (2.1%), Bay/Delta (1.6%), and Northeast/Northcentral California (1.2%) areas in obsidian reuse.
At COL-160, a site in the North Coast Ranges, Waechter and Origer (1993) found an anomalously high proportion of obsidian specimens with multiple hydration bands: 28 out of 95 specimens tested (29.5%). The relationships of the site to travel corridors and to potentially impervious ethnic boundaries were considered as potential explanations. The overall range of the hydration measurements on the smaller bands (3.2 to 7.0 microns, for Borax Lake obsidian) indicated a long occupation of the site, yet the difference between hydration bands on any one obsidian specimen was no greater than 3.0 microns and averaged only 1.8 microns. This suggested that usable obsidian had tended to be recycled promptly. Multiple bands were somewhat more frequent on specimens from the later period of occupation, but such bands were not confined to that period. A previous suggestion by Skinner — that a technological change to the use of bow and arrow had made the scavenging of previously unusable small pieces of obsidian attractive — apparently could not account for all of the scavenging. Also noted were potentially misleading effects from sampling error and differences in laboratory techniques and reporting.
Sharon McFarland (2000) collected hydration readings on 941 specimens from 129 sites in San Diego County. Thirty-one of the specimens had multiple hydration rims, amounting to 3.3%, or slightly less than for the Waechter and Origer’s sample of the South Coast region as a whole.
The table below presents data on 42 specimens with multiple hydration rims. The maximum difference between the rims on a specimen is 10 microns, the mean is 2.9 microns, and the median is 1.8 microns.
| Site | Hydration Sample Size |
Obsidian Source |
Multiple-Band Readings |
References |
| SDI-39 | 12 | Obsidian Butte | 1.8 + 2.6 | Berryman and Roth 1993; Gross and Robbins-Wade 1999 |
| “ | 2.2 + 2.6 + 3.4 | |||
| “ | 2.4 + 2.9 | |||
| “ | 2.8 + 3.4 | |||
| SDI-217 | 27 | Obsidian Butte | 1.6 + 6.7b | Waugh 1986 |
| “ | 4.9 + 7.6 | |||
| SDI-674 | 18 | Obsidian Butte | 2.7 + 4.8 | Rosen 1984 |
| “ | 3.4 + 12.8 | |||
| “ | 3.3 + 3.8 + 6.7 | |||
| SDI-955 | 2 | Obsidian Butte | 1.2 + 4.6 | McFarland 2000 |
| SDI-2532 | 3 | undetermined | 2.8 + 12.8 | Cook and Fulmer 1980 |
| SDI-2537 | 129 | Obsidian Butte | 1.7 + 2.5 | Bouey and Onken 1986; McDonald 1992 |
| “ | 1.8 + 2.6 | |||
| “ | 2.3 + 4.0 | |||
| “ | 3.3 + 3.8 | |||
| “ | 3.8 + 7.5 | |||
| “ | 4.1 + 10.5 | |||
| SDI-4358 | 3 | Coso | 4.9 + 5.9 + 7.6 | Gallegos and Kyle 1991 |
| SDI-4530 | 47 | Obsidian Butte | 1.0 + 2.0 | McFarland 2000 |
| “ | 1.3 + 2.1 | |||
| Coso | 1.3 + 2.5 | |||
| “ | 3.9 + 7.4 + 9.3 | |||
| SDI-4608 | 30 | Truman/Queen | 5.3 + 7.0 | McFarland 2000 |
| SDI-5130 | 32 | Coso | 1.6 + 10.8 | McFarland 2000 |
| Casa Diablo | 1.7 + 9.8 | |||
| undetermined | 7.2 + 10.8 | |||
| SDI-8493 | 10 | undetermined | 1.0 + 3.8 | Graham 1981 |
| SDI-8594 | 3 | Coso | 5.2 + 6.2 | Corum 1986 |
| SDI-9243 | 48 | Obsidian Butte | 1.3 + 3.1 | Carrico et al. 1994 |
| SDI-9649 | 8 | undetermined | 2.9 + 4.4 | Koerper 1986; Koerper et al. 1991 |
| Coso | 4.5 + 6.0 | |||
| SDI-10156 | 17 | Obsidian Butte | 1.9 + 4.4 | Strudwick 1998 |
| SDI-10726 | 3 | Coso | 1.6 + 11.0 | McFarland 2000 |
| SDI-10998 | 6 | Obsidian Butte | 5.1 + 7.3 | Laylander 1992a |
| SDI-11767 | 3 | Coso | 4.5 + 5.2 | Cooley and Mitchell 1996; Kyle and Gallegos 1995 |
| SDI-12557 | 15 | Obsidian Butte | 2.7 + 3.9 | Bissell 1997 |
| SDI-12628 | 3 | Coso | 4.9 + 8.6 | McFarland 2000 |
| SDM-W-230 | 27 | Obsidian Butte | 2.6 + 3.7 | Gross 1991:personal communication |
| Coso | 5.8 + 6.9 | |||
| SDM-W-593 | 8 | undetermined | 5.9 + 8.2 | Meighan and Russell 1981 |
| “ | 17.5 + 19.8 | |||
| SDM-W-1556 | 8 | undetermined | 6.4 + 7.2 | O’Neil 1982 |
PROSPECTS
Future archaeological investigations may be able to confirm that the rate of obsidian reuse in San Diego region was relatively low compared to that in some regions of primary quarrying (North Coast Ranges and Eastern Sierras) but higher than in other parts of California. It may be possible to determine whether there was a generalized increase or decrease in reuse through time, or whether there were episodes of more intensive scavenging, for instance during the period when the bow and arrow was replacing the atlatl and dart or when the Obsidian Butte source was inaccessible due to the presence of Lake Cahuilla. Different rates of reuse may be determined for obsidian from the Coso and Obsidian Butte sources. Studies may determine whether scavenged material came primarily from the locations where the items were ultimately discarded, as indicated by matching between single-band hydration measurements and the thicker bands on multiple-band specimens, or whether the obsidian had been collected from other sites.