THE CASUAL LOOK AT FORT IRWIN:
EDGE TOOLS AND PREHISTORIC MOBILITY
|Paper presented at the 2001 Kelso Conference on the Archaeology of the California Desert, Hemet (corrected 9/08)|
Abstract: A concept of "casual" or "expedient" tool types and assemblages has been employed in archaeological investigations at Fort Irwin over the last decade, and relationships between degrees of "casualness" and varying mobility strategies have been inferred. The foundations for these characterizations and their interpretations are worth reevaluating. There is reason to suppose (a) that criteria other than the ones commonly employed may be more appropriate for capturing the "casual" dimension, (b) that the proposed prehistoric trend toward increasing casualness may not be valid, and (c) that the implications of this dimension with respect to mobility may not be the ones commonly proposed. Some possible directions for future investigations are also suggested.
A distinction between "formed flake tools" (or FFTs) and "casual flake tools" (or CFTs) has been widely applied to the analysis of lithic assemblages from Fort Irwin and surrounding areas during the past decade. Links have been proposed between the ratio of these two classes and prehistoric changes in mobility strategy. Formed flake tools, which are more common in earlier assemblages, have been said to be indicative of greater mobility, while casual tools have been considered characteristic of less mobile groups.
Three propositions which are at least implicit in this model are worth reexamining:
First, is it "casualness" that differentiated casual from formed flake tools? Two different--if related--meanings for "casual" need to be considered: (a) casualness as a lack of effort at refinement in tool manufacturing, and (b) casualness as the discarding of tools after minimal use.
- (1) that, functionally speaking, the distinction between FFTs and CFTs is primarily a distinction in casualness or expediency;
- (2) that there was a prehistoric trend through time toward increasing casualness or expediency in tool manufacturing and use in the region; and
- (3) that greater casualness or expediency was indicative of decreased residential mobility.
Casualness in tool manufacturing may be considered first. CFTs, for the most part, are flakes that were used substantially as they came off the core, whereas FFTs show definite evidence of intentional flaking. This clearly constitutes a difference in manufacturing effort. However, the crucial question is whether making a formed flake tool rather than merely using an unmodified flake involved significant extra manufacturing effort. It seems likely that the extra time and effort involved in preparing most FFTs was trivial--probably typically less than a minute to shape an edge, if a knapping tool were already at hand. If the functioning of a flake tool could be improved at such a small cost, it seems unlikely that even the most expedient tool user would have begrudged the extra effort that was involved. If it is true that the difference in manufacturing cost was trivial, then CFTs presumably were not used in their unmodified form in order to avoid the added manufacturing costs, but because the "improvements" were unnecessary or even undesirable for the purposes at hand.
The other meaning for casualness is that casual tools were discarded after only brief use. Did FFTs start out as CFTs, whose edges were then subsequently resharpened to prolong their use-lives? This is likely to have been true in some instances, but as a generalization about most FFTs it is not persuasive. One argument against such an interpretation is that, on the average, FFTs are consistently larger than CFTs in most archaeological assemblages, whereas the opposite might be expected if the difference were primarily one of mass reduction through resharpening. Another test of the generalization would be to consider the frequency with which FFTs still contain edges that are usable but unused. Such edges should probably be rare if FFTs were primarily CFTs that had required resharpening of their worn edges. On the other hand, suitable but unused edges might be common on FFTs if the worked edges were produced not to resharpen them but instead to achieve specific objectives in edge form. Information on unused tool edges has not been regularly collected for Ft. Irwin assemblages. An impressionistic look at the FFTs in a Middle Holocene assemblage from Garlic Spring suggests that unused edges were fairly common on such tools.
To evaluate casualness in the use and discard of flake tools, there are other criteria that would probably work better than the conventional dichotomy between FFTs and CFTs. Possibly the most practical index is the number of modified edges per tool, which should be low with casual tool use but high for tools with prolonged use-lives. Another criterion, already mentioned, is the proportion of unused but usable tool perimeter. A third possible criterion would be the intensity of use wear or damage present on individual edges. Finally, a fourth criterion is the diversity of edge forms in individual tools. Casually-discarded tools might tend to have been used for only a single function, served by a single type of edge. On the other hand, if tools were carried along on their makers' travels, there might have been a premium on multifunctionality, or the use of "Swiss Army rocks". Some previous assessments of tool multifunctionality at Ft. Irwin have been unpersuasive, either because they were merely intuitive or because some of the indices that were used--such as contrasts between convex and straight edges, or regular and irregular edges--are not convincing as functional contrasts. More promising indicators of different tool functions might be edge angle and concave vs. non-concave edge form. Table 1 presents some evidence on multifunctionality, based on data reported for nearly 300 FFTs from the Rogers Ridge Site (CA-SBR-5250). It is notable that more than one-third of the FFTs contained only a single edge. Among the multi-edged tools, the relatively scarce concave edges were not evenly spread among different tools, but actually tended to be slightly clustered on single tools, although not significantly more so than might have occurred with a random distribution of the edges. As to edge angles, the angles of different edges on the same tool were more similar to each other than would have occurred 95% of the time if the observed edge angles had been distributed randomly among the various tools. Both of these patterns--for edge shape and for edge steepness--point toward a degree of specialization in tool function, or at least they give no support to the hypothesis of a tendency toward multifunctionality.
Table 1. Evidence Concerning the Multifunctionality of Formed Flake Tools
from the Rogers Ridge Site (SBR-5250).
All FFTs 299 Multi-edged FFTs 191 All Edges on Multi-edged FFTs 488 Concave Edges on Multi-edged FFTs 66 Concave Edges on FFTs with More than One Concave Edge 20 3 14.3 Multi-edged FFTs with No Concave Edges 135 4 132.4 Mean Difference in Edge Angles on an FFT 14.2o 5 15.1o1 Data from Hall (1993). FFTs lacking data on some edge attributes have been excluded, as has one FFT with an apparent typographic error concerning an edge angle.
2 Based on 10,000 computer simulation runs which randomly matched the observed edge angles and the percentage of concave edges with tools having the observed numbers of edges.
3 Multiple concave edges on the same tool are somewhat more common that would be expected with randomized matches of edge types to tools, suggesting a trend toward tool specialization rather than multifunctionality. However, the patterning is not statistically significant.
4 Multi-edged tools lacking any concave edges are slightly more common than would be expected with randomized matches, but again the departure from randomness is not statistically significant.
5 Edge angles on the same tool were more similar to each other on the actual tools than in randomized matches in more than 95% of the simulation runs. This argues for a significant tendency toward tool specialization rather than multifunctionality.
Turning away from flake tools for a moment, handstones or manos are an alternative tool class that seems to provide better indices for both varieties of casualness. The use requirements of most handstones were probably relatively simple and uniform, and the differences observed among handstones were probably not differences between functional types. The two attributes most commonly documented for handstones are (a) the presence or absence of tool shaping and (b) the presence or absence of more than one grinding surface. These attributes can be directly interpreted as indices of casualness. Handstone shaping, in contrast to flake tool shaping, probably would have involved an appreciable investment of extra manufacturing effort. Apart from possible aesthetic motives, shaping was probably done primarily in order to increase tool efficiency, through improving the tool's handling and perhaps to get a higher ratio of grinding surface area to tool mass, which may have made the milling task a little less tiring. Whether or not the investment in shaping would have been worthwhile would probably have depended upon the expected length of the use life for the tool. Unshaped handstones were evidently casual tools in that they were used and discarded without making the investment in shaping.
Multifacial handstones, in contrast, maximized the use made of materials (i.e., suitable cobbles), which in some cases may have been in short supply locally or costly to procure. Unifacial handstones were casual tools in that they were discarded generally without making full use of their milling potential. It is true that, in some cases, a cobble may not have more than a single potential milling surface. It is also true that the potential use life of a milling surface might have varied substantially according to the particular lithic material involved, and that some unifacial handstones probably experienced more use than some bifacial handstones. However, on the average, it is probably correct to say that bifacial or trifacial handstones were more thoroughly used--and more thoroughly used up--than unifacial handstones, and that the latter were in this sense relatively casual tools.
For the first of the three propositions being reexamined, the conclusion proposed here is that casualness or expediency is not well captured in the usual distinction between FFTs and CFTs, and that there are better measures of casualness available, both in alternative attributes of edge tools and for other tool classes, particularly groundstone.
The second proposition is the claim that there was a trend through time toward increasing casualness or expediency in tool use in the prehistoric Mojave Desert. Archaeological evidence seems to support the claim that there was a trend through time toward a higher ratio of CFTs to FFTs. However, if the first argument is correct, such a trend is more likely to mirror some other underlying pattern, such as a decrease in the steepness of the desired tool edges, and it is more likely to have arisen from a shift in tool functions--perhaps toward more use in cutting and less use in scraping--rather than from increasing casualness.
The data which are available from Ft. Irwin for testing the proposed alternative indices of tool casualness are limited, especially with regard to later-period assemblages. There is not an adequate basis at hand to evaluate completeness of edge tool use, intensity of edge modification, or tool multifunctionality in early vs. late assemblages. For a few of the other indices, there are at least some preliminary indications:
(a) Do later edge tools typically show fewer modified edges than earlier flake tools? Table 2 summarizes data on this dimension for about 750 tools from 20 sites in the Nelson Basin. The trend that is found is in the predicted direction, but it is too slight to be significant, even at the 90% confidence level, according to a chi2 test.
Table 2. Numbers of Edges on Early- and Late-Period Flake Tools
from Nelson Basin Sites.
FFTs CFTs Combined CA-SBR- No. of Tools No. of Edges Mean No. of Edges No. of Tools No. of Edges Mean No. of Edges No. of Tools No. of Edges Mean No. of Edges Early 5029 14 30 2.14 13 22 1.69 27 52 1.93 5042 5 17 3.40 5 7 1.40 10 24 2.40 5044 17 35 2.06 6 9 1.50 23 44 1.91 5047 103 233 2.26 50 95 1.90 153 328 2.14 5255 10 31 3.10 7 11 1.57 17 42 2.47 5262 9 33 3.67 6 15 2.50 15 48 3.20 5263 14 31 2.21 18 34 1.89 32 65 2.03 2355 204 488 2.39 57 94 1.65 261 582 2.23 2356 112 253 2.26 55 102 1.85 167 355 2.13 Total 488 1151 2.36 217 389 1.79 705 1540 2.18 Late 4171 7 11 1.57 3 3 1.00 10 14 1.40 5015 1 3 3.00 2 2 1.00 3 5 1.67 5266 3 7 2.33 2 2 1.00 5 9 1.80 6214 - - - 1 2 2.00 1 2 2.00 6216 - - - 1 2 2.00 1 2 2.00 6217 - - - 4 6 1.50 4 6 1.50 6218 1 1 1.00 2 5 2.50 3 6 2.00 6219 1 3 3.00 1 2 2.00 2 5 2.50 6223 6 10 1.67 5 8 1.60 11 18 1.64 6235 1 3 3.00 4 14 3.50 5 17 3.40 6236 1 2 2.00 2 2 1.00 3 4 1.33 Total 21 40 1.90 27 48 1.78 48 88 1.83Data from Basgall (1993).(b) Are later handstones less frequently shaped than earlier handstones? Some limited data, presented in Table 3, suggests the opposite: that later handstones were more frequently shaped. A chi2 test indicates that the contrast is statistically significant, although the sample size--about 100 specimens from two dozen sites--should certainly be enlarged before any general conclusion is drawn.
Table 3. Attributes of Handstones from Assorted Ft. Irwin Assemblages, by Period.
Unshaped Shaped Unifacial Multifacial Early CA-SBR- 2355, 2356, 5044, 5047, 5255, 5262 1 7 2 7 2 CA-SBR- 4562 2 4 3 4 3 CA-SBR- 2348 3 29 5 10 25 CA-SBR- 5251 (part), 5256, 5369 4 10 8 15 2 CA-SBR- 8984, 10319 5 1 4 2 3 Total 51 22 38 35 70 % 30 % 52 % 48 % Late CA-SBR- 4171, 5266, 6214, 6217 1 3 1 3 1 CA-SBR- 5248, 5367, 5380 4 4 12 8 9 CA-SBR- 5002, 8291, 8292 6 2 1 3 1 CA-SBR- 10111, 10116 7 2 1 3 0 Total 11 15 17 11 42 % 58 % 61 % 39 % chi2 = 6.21 (significant
at 0.05 level)
chi2 = 0.61
(not significant)1 Nelson Basin sites; data from Basgall (1993).(c) Are later handstones more often unifacial than earlier handstones? In this case, the limited sample shows a slight shift in the predicted direction, although the pattern is not statistically significant (Table 3).
2 Awl Site; data from Basgall and Hall (1993).
3 Goldstone Site; data from Basgall and Hall (1994).
4 Tiefort Basin sites; data from Hall (1993).
5 Garlic Spring sites; data from Laylander and Victorino (2001a).
6 Langford Well sites; data from Foster et al. (2001).
7 Tortoise Critical Habitat sites; data from Laylander and Victorino (2001b).
In general, there does not seem to be persuasive evidence as yet for the proposed trend toward increasing casualness in tool use at Ft. Irwin.
The final proposition to be reexamined is that a higher proportion of casual tools is indicative of reduced prehistoric mobility. Although such a link has often been asserted or assumed, a clear rationalization for it has usually not been offered. The standard explanation seems to be that highly mobile people were less certain that they would have suitable lithic raw materials available to them at any given time. Therefore they had to carry their tool kits with them, and for efficiency such tool kits had to be limited to a few tools that were well-made, heavily-used, and versatile.
Such an explanation may work if it is assumed that most of the tools recovered archaeologically had been carried around in residential travels, and if it is assumed that raw lithic material was more costly or more uncertainly available for more mobile people, despite their mobility. As alternatives to those assumptions, it may be proposed that carrying tools during residential moves was not the dominant pattern, and that relatively sedentary people had to go farther out of their way to get good toolstone than did more mobile people. If a site were going to be occupied for an extended period of time, or if it were going to be revisited frequently or dependably, as would be the case with more sedentary settlement strategies, the use-lives of tools ought to have been longer, because the tools could be kept in continuous use longer, and they could be cached at the site for reuse later, rather than merely being discarded. With expected tool use-lives being longer, it would also have been more worthwhile to invest some extra effort up front on manufacturing costs, in order to make really efficient tools. According to this reasoning, casualness in tool manufacturing and tool discard were likely to have been higher among more mobile people than among sedentary ones, rather than the reverse. At any rate, the third proposition, that there is a positive causal link between sedentism and casual tool use, does not merit being treated as an established fact at this point.
In conclusion, a few suggestions for future directions in the handling of these issues are offered. One set of suggestions concerns potential experimental, replicative studies. It would be useful to document the amount of work involved in making formed flake tools and in shaping manos. It would be interesting, but somewhat more difficult, to try to test and quantify the functional superiority of a shaped mano over an unshaped one. Other replicative studies might test the differences among flake tools in such attributes as edge angle, edge shape, and edge position, in relationship to their effectiveness in performing different tasks.
Other suggestions concern the ways archaeological assemblages are analyzed and reported. It would be worthwhile to reconsider the attributes that are to be routinely reported. These should be evaluated on the basis of the three criteria: (a) their standardization, to make possible inter-collection comparisons; (b) their replicability by different analysts, for the same purpose and to minimize bias; and (c) their relevance to valid interpretive issues. Table 4 summarizes several edge tool attributes, suggesting possible criteria for making them more replicable and commenting on their interpretive relevance.
Table 4. Edge Tool Attributes, and Suggested Criteria and Interpretations for Them.
Attributes Suggested Criteria Interpretive Values tool size weight probably correlated with tool retention and material availability flake-based tool (vs. core-based) recognizable ventral flake scar probably of minimal significance worked edge (vs. only utilized) some scars >2 mm long probably correlated with definite intentional origin (rather than postdepositional trampling, etc.) single edge (vs. multiple) modified edge is continuous, <90o change in orientation probably correlated with casual tool use multiple edge types (vs. single type) e.g., both acute and steep, both concave and convex/straight probably correlated with tool retention acute edge (vs. steep) <55o at 5 mm probably correlated with function (e.g., cutting rather than scraping) concave edge(vs. straight/convex) radius of curvature <4 cm outward probably correlated with function (e.g., working on sticks or bones rather than flesh or hides) convex edge (vs. straight) radius of curvature <4 cm inward probably of minimal significance even edge (vs. irregular) no criterion suggested probably of minimal significance unifacial modification (vs. bifacial) flake scars on both sides of a given edge probably of minimal significance ventral modification (vs. dorsal) modification on surface with bulb of percussion probably of minimal significance end position of edge (vs. side) principal modified edge is distal probably of minimal significance; possibly correlated with manner of hafting slight modification (vs. intensive) fewer than 8 flake scars on any cm of modified edge probably correlated with casual tool use incomplete tool use (vs. complete) >25% of usable perimeter shows no modification probably correlated with casual tool use
Jeanne Binning, Sinead Ni Ghabhlain, and Deborah Huntley provided helpful comments on an earlier draft of this paper.
Thanks also to Claude Warren and Joan Schneider for their encouragement.
Basgall, Mark E. 1993. The Archaeology of Nelson Basin and Adjacent Areas, Fort Irwin, San Bernardino County, California. Far Western Anthropological Research Group, Davis.
Basgall, Mark E. and M.C. Hall. 1993. Archaeology of the Awl Site, CA-SBR-4562, Fort Irwin, San Bernardino County, California. Far Western Anthropological Research Group, Inc., Davis.
Basgall, Mark E. and M.C. Hall. 1994. Archaeological Investigations at Goldstone (CA-SBR-2383): A Middle Holocene Occupation Complex in the North-Central Desert, California.Far Western Anthropological Research Group, Inc., Davis.
Foster, Karen, Sean Hess, and Craig Woodman. 2001. Late Holocene Archaeology of Langford Well Lake. Science Applications International, Santa Barbara.
Hall, M.C. 1993. Archaeology of Seven Prehistoric Sites in Tiefort Basin, Fort Irwin, San Bernardino County, California. Far Western Anthropological Research Group, Davis.
Laylander, Don and Ken Victorino. 2001a. Archaeological Evaluation of the Garlic Spring Sites (CA-SBR-8,983, CA-SBR-8,984, and CA-SBR-10,319), Fort Irwin, San Bernardino County, California. ASM Affiliates, Encinitas.
Laylander, Don and Ken Victorino. 2001b. Archaeological Evaluation of Four Sites (CA-SBR-10,105, CA-SBR-10,111, CA-SBR-10,112, and CA-SBR-10,116) in the Tortoise Critical Habitat Area, Fort Irwin, San Bernardino County, California. ASM Affiliates, Encinitas.
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