Manos

Manos, the upper handstones used in stone-on-stone grinding, are abundant in many San Diego assemblages. They have generally been recognized as artifacts on the basis of polish, flattening, and striations on flat to moderately convex surfaces. Although most commonly associated with seed processing, manos were used on a range of other materials, including small animals and minerals as well as other plant parts. It is generally thought that milling was primarily a female activity in the region prehistorically.

From a chronological perspective, many researchers have suggested that manos were absent or very rare in assemblages belonging to the early Holocene San Dieguito complex (e.g., Chartkoff and Chartkoff 1984; Davis 1969; Moratto 1984; Moriarty 1966; Rogers 1939, 1940; Warren 1964; Warren and True 1961). However, that suggestion has also been challenged (e.g., Warren 1987; Warren et al. 2008).

Analyses of mano attributes have attempted to understand the ways in which manos were procured and manufactured, the specific manner in which they were used, the purposes for which they were used, the relative intensity of their use in different contexts, and the circumstances of their discard, exhaustion, curation, or reuse. One of the most thorough local considerations of mano attributes was a study by Richard H. Norwood (1980), based on the milling tools recovered from the Reading Site (SDM-W-1504). Potentially significant mano attributes identified by Norwood and others include the following:

— Size. Norwood (1980:103) suggested that “heavier milling tasks might require heavier manos” and that contrasts in mano weight might indicate contrasts in the resources being milled. In his study of manos from surface and subsurface contexts at the Reading Site, Norwood reported an apparent increase in average mano weight through time. Size would presumably also be the basis for differentiating “single-handed” from “two-handed” manos; Malcolm J. Rogers (1945:187) reported that single-handed manos were characteristic of the Yuman I period, that two-handed manos were characteristic of Yuman III, and that Yuman II assemblages included both forms.

— Completeness. Norwood estimated the completeness of manos in 25% increments. He suggested that contrasts in this attribute might be related to contrasts in original mano size, in resilience, and in postdepositional factors such as weathering, disking, and vehicle activity at the site.

— Rock Type and Grain Size. The type of material used for manos may have been reflected the desired durability of the tools, the degree of concern with grit being added to milled food, and the relative accessibility of suitable material sources. An apparent shift through time toward the use of finer-grained rock for manos was reported at the Reading Site, which “may be an indication of a shift in milling function” (Norwood 1980:107).

— Plan View Shape. Reported plan view shapes for local manos are oval, circular, rectangular, and biconical. Differences in mano shape may reflect differences in the available cobbles, the shapes of metates, or the manner in which milling was performed.

— Cross Section Shape. The degree of flattening and shouldering on manos may reflect the extent of their use. Symmetry or asymmetry in shouldering may indicate patterns in the way manos were used. Manos with strongly convex faces may have served different functions or have been used in a different manner than manos with flat faces. Wedge-shaped manos, with strongly converging faces, have been commonly distinguished from manos with parallel faces, and the two types may have been used differently.

— Number of Faces. Manos are commonly classified as unifacial, bifacial, or, in rarer cases, trifacial. The majority of the manos in most San Diego County assemblages are bifacial. A high proportion of unifacial manos at a site may reflect a shorter span of site occupation, with tools having been abandoned after relatively light use rather than being reused over a more extended period of time.

— Similarity of Faces. Norwood noted that most of the bifacial manos from the Reading Site were dissimilar in the attributes of their two faces. The implications of this observation were not explored; it may reflect a regular pattern of using a single tool for diverse functions.

— Polish. As Norwood noted, the degree of polish on a mano may relate to how extensively it was used, how recently and heavily it was pecked for resharpening, and the nature and orientation of the rock’s mineral grains. The degree of natural, pre-use polishing is also a factor. Relative polish can be expressed either in terms of the relative intensity of the polish or the proportion of the face on which it is present, or some combination of the two.

— Striations. The presence of macroscopically observable facial striations may indicate the extent of mano use, the hardness of the material being milled, or the extent to which mineral grit was being allowed to mix with the milled substance. A consistent orientation in the striations may indicate the axis along which the mano was moved during milling.

— Surface Residues. Residues of milled materials may be manifested in surface discoloration, the recovery of materials through washing and fine sorting, and chemical signatures. The identification of surface residues may be the most direct method for establishing the functions of manos.

— Facial Modification. According to Norwood (1980:108), facial pecking “is assumed to be related to the maintenance of a milling face which is effective for the milling of specific materials.” It is not clear whether contrasts in the presence or absence of observable pecking should be attributed to the specific materials that were being milled, the overall amount of mano use, or the stage within the cycle of use and sharpening at which the specimen was discarded or abandoned.

— Edge Grinding. Norwood noted that edge grinding might accompany mano shaping, but that alternatively it might “be indicative of a rolling rather than a linear grinding motion.” Presumably such contrasting patterns of motion might reflect either contrasts in the specific tasks that were being performed or in the cultural norms for how a task should be performed.

— Edge Battering and Crushing. Tools that combine the attributes of manos and hammerstones have frequently been reported in San Diego County assemblages. The use of a tool both as a mano and as a hammer may have occurred during the performance of a single task, or the tool may have been used for different functions on different occasions.

— Exposure to Fire. This attribute may be manifested by blackening, discoloration, sharp and irregular breaks, or surface crazing. Intentional exposure to fire would probably not relate to the primary function of manos as milling tools, but would reflect their use, in either whole or broken condition, for such tasks as stone boiling or lining hearths or roasting pits.

Micah J. Hale (2006) quantified the attributes of ground stone artifacts at sites in northern San Diego County, with the specific objective of evaluating evidence concerning subsistence intensification. The attributes considered by Hale included multiple used surfaces, shaping, regularity of shape, smoothness, polish, striations, and pecking. The study found that the artifacts in earlier (Archaic; Middle Holocene) assemblages were more intensively used than those in later (Late Prehistoric; Late Holocene) assemblages.

PROSPECTS

Future archaeological investigations may be able to identify more clearly the purposes for which manos were used, as well as changing patterns in the ways they were manufactured, used, maintained, curated, and discarded. Evidence useful in addressing these issues will include standardized data on tool size and shape, rock type and grain size, the number and configuration of used surfaces, patterns of shaping and use wear, surface residues, and tool condition. Also relevant will be the ecological, chronological, functional, and social contexts from which manos are recovered. Replicative experiments may be able to identify manufacturing and maintenance costs, effectiveness for various tasks, and characteristic wear patterns.