Unifacially shaped or use-damaged stone tools, generally termed scrapers, frequently constitute the most abundant class of lithic artifact, apart from debitage, in the prehistoric assemblages of San Diego County. Perhaps no other prehistoric lithic tool class in the region has been the subject of such extreme typological differentiation. Explicitly or implicitly, scraper tool types have been related to distinctions in chronology, cultural tradition, activity, and tool use cycle. Inconsistencies and ambiguities in the ways scraper types have been defined may have affected many of the descriptions and interpretations of local prehistoric tool assemblages.
Elaborate scraper typologies have been employed by some San Diego archaeologists, notably by Malcolm J. Rogers (1929, 1939, 1966); by D. L. True, Claude N. Warren, and their collaborators (True 1966, 1970, 1980; True et al. 1974, 1991; Warren 1964, 1966; Warren and True 1961; Warren et al. 1961); and by some later archaeologists, including Ronald V. May (1975), Russell L. Kaldenberg (1982), and Dennis H. O'Neil (1982). A range of attributes have been suggested as significant in classifying these artifacts:
-- Shaping vs. Use Damage. Tools that show evidence of purposeful shaping on their working edges have been distinguished from cores or flakes that show only modification resulting from use. The distinction between shaping and use damage seems to have been based most commonly on the size of the flake scars produced. Unresolved problems exist in trying to distinguish the modifications made to shape working edges or produced during use from modifications that resulted from preparing cores for flake removal or from accidental postdepositional damage.
-- Tool Size. The sizes of tools have been characterized on the basis of their weight or their maximum dimension. For example, Kaldenberg categorized "thumbnail scrapers (micro-scrapers)" as less than 5 centimeters in length. Rogers (1929) seems to have used size as a primary criterion in distinguishing scraper planes from scrapers; he also distinguished "large" and "small" planes (Rogers 1966). True and his collaborators distinguished scraper planes from domed scrapers primarily on the basis of the larger size of the former. Roy A. Salls (1985) apparently distinguished scraper planes from scrapers on the basis of the steeper edge angle of the latter; however, in experiments using replicated tools to pulp yucca leaves for fiber, he noted that the scraper planes were more efficient than the scrapers because of the former's "size and weight" (Salls 1985:103).
-- Tool Shape. The shape of scrapers, in plan view, in profile, or both, has frequently been considered diagnostic. Among the tool shapes distinguished by Rogers were rectangular, triangular, irregular, discoidal, and beaked plan views and tabular, keeled, and domed profiles. Makoto Kowta (1969), in an influential study, defined scraper planes on the basis of the ratio of tool height to length. Kowta also discriminated some 16 other unifacial tool types, primarily on the basis of tool shape. True and his collaborators (1991:21) defined keeled scrapers as "elongate in outline with a narrow base [and] a steep-sided angular top," but they noted that this configuration might be merely accidental. They distinguished conventional and irregular varieties of domed scrapers, the former having "round or oval outlines that appear to be the result of deliberate shaping" (True et al. 1991:20). Conventionalized and irregular flake scrapers were also distinguished, although the "mental templates" evidenced in the former were not specified. Some chronological significance for these distinctions was hinted. O'Neil separated out unifaces made from blade (linear) flakes.
-- Tool Base. Scrapers that were cores have frequently been differentiated from those that were flakes.
-- Location and Character of Cortex. Cortex-based scrapers, whose planar ventral surfaces consist of cobble cortex, have been distinguished. Scrapers made from teshoa flakes have also been noted.
-- Number of Worked Edges. Kaldenberg differentiated tools with one and two worked edges.
-- Edge Angle. Planes were distinguished from scrapers by O'Neil, Salls, and others by the criterion that planes have vertical or nearly vertical working edges whereas scrapers have more acute working edges.
-- Edge Shape. Tools with concave, straight, and convex working edges have frequently been distinguished. Kaldenberg also differentiated "notched" and "denticulated" scrapers.
-- Location of Functional Edges. End scrapers and side scrapers have been distinguished. Kaldenberg differentiated specimens with two worked edges according to whether the edges were adjacent or non-adjacent.
-- Use Wear. Salls reported distinctive use wear, primarily microscopic polish, on some archaeologically recovered scraper planes and on replicated planes used to pulp yucca leaves but not on archaeologically recovered scrapers. He noted but rejected the proposal of Brantley J. Jackson (1977) that artifacts interpreted as scraper planes were merely cores with "wear" from platform preparation rather than from use.
Several possible functions for unifacial tools have been suggested:
-- Pulping Agave and Yucca Fiber. Rogers (1939), Kowta, and Salls argued that this was the function of scraper planes. The interpretation was based upon (a) ethnographic reports for the southern Kumeyaay, (b) the archaeological distribution of the tools in space and in time, (c) observed tool wear and its correspondence to wear on replicated tools used for this purpose, and (d) experimental confirmation of the effectiveness of the tools in performing this task.
-- Woodworking. Aschmann (1959) and Kowta suggested that scraper planes were used to plane wooden tablas (religious objects used in the Yuman- and Cochimí-speaking areas of Baja California) and wooden tools and weapons.
-- Sharpening Milling Equipment. Kowta (1967:52) asserted that "there seems to be little question that at least some...scraper planes were used to roughen grinding stones."
Future archaeological studies may be able to identify the range of functions in which scraping tools were used and the significance of scraper variability in terms of function, chronology, cultural tradition, lithic material characteristics, and use life. Evidence bearing upon these issues will potentially include tool size and shape, edge location and configuration, evidence of modification from shaping or use, and identifiable residues. Also relevant are the ecological, chronological, functional, and social contexts from which the artifacts are recovered. Replicative experiments may be able to identify manufacturing and maintenance costs, effectiveness for various tasks, and characteristic wear patterns.