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Show variation both synchronically and diachronically is crucial to further interpretations of prehistoric human behavior. Assemblage-level variability cannot be easily accounted for by technological, functional, and cultural factors alone. Other important sources of variation at the assemblage level include those related to variation in the duration and intensity of site occupation or reoccupation (occupational variability), those related to variation in mobility patterns and the organization of subsistence-settlement systems (organizational variability), and variability in depositional and post-depositional processes (variability in formation processes). Therefore, interpreting inter-assemblage variability requires that the many factors that contribute to variation be recognized and controlled for (see Sullivan 1987). Raw Material Sources and Use Stone displays a great diversity of physical properties that prehistoric people understood and used to their advantage. Properties such as crystal structure or the lack thereof, density, grain size, and hardness allow for a wide range of potential usages and influence the range of purposes best suited for a specific material due to mechanical and production constraints. The geographical distribution of materials and their relative abundances and mode of occurrence (nodule size, etc.) can also affect what materials are used for which purposes and how the materials are modified to produce tools. In certain geographical settings the choice of raw material for stone tools can be quite limited, and this might be the initial impression for the region traversed by the N16 ROW. After all, the area appears quite geologically uniform, consisting of Navajo Sandstone and the Kayenta Formation. As outlined in Chapter 5 of Volume I (see also Geib and Ambler 1985), the N16 project area actually offers a great diversity of raw materials for all types of stone artifacts. This diversity results from the geologic structure of the region (Cooley et al. 1969; Gregory 1916, 1917) as well as the Colorado and San Juan Rivers with their Pleistocene cobble deposits (Cooley 1960). Geology and geomorphology create a complex and highly patterned lithic landscape for the northern Kayenta region and the occupants of the NMRAP sites had differential access to the various stone types depending on mobility patterns, settlement type, and functional requirements. In such circumstances, one reasonable hypothesis is that raw material selection was partially conditioned by functional suitability. Phagan (1982:28-29) has spelled out the essential reasoning for how grain size and silicification affect functional suitability, which can be paraphrased as follows: with increasing grain size there should generally be a change in tasks from cutting, piercing, and scraping to tougher jobs such as grinding, pounding, chopping, and abrading. For fine cutting of soft material such as meat or hide a noncrystalline highly siliceous material such as obsidian would be preferred, but for sawing bone a tough microcrystalline chert or even coarser quartzite would be preferred. Preferences extend to rocks for other tasks as well, such as raw material for grinding tools. Different textures for grinding tools have been ethnographically documented as having relevance to Puebloan groups for processing corn (Bartlett 1933). Within this framework, raw materials for grinding tools would be specially selected based on texture in order to meet corn processing needs. An important part of the functional suitability equation concerns how stringent the demands are for a given task. Because some tasks have minimal requirements, almost any stone will suffice. In such a case, the lithic landscape is rich and opportunities abound. A pecking stone provides a useful example. Almost any dense hard rock will suffice for this task (minimal requirements) and little production investment is needed, with cobbles often working effectively simply as found. As such, raw materials suitable for pecking stones can be secured nearly anywhere, with no need to travel far, especially outside the normal foraging area around a habitation. Pecking stones are good examples of expedient tools, the material for which can be acquired casually close to home-just send the kids out to find a hard rock-with little or no need for production investment. Shaving the hair from one's head is at the opposite end of the spectrum when it comes to stringent demands on stone raw material. This task is difficult to achieve except with volcanic glass, and obsidian has very limited distribution on the Colorado Plateau. The lithic landscape appears severely constrained when there is a desire for a razor sharp edge. Because this task has low tolerance for substitution, one either does not shave or one finds a means to procure obsidian from great distances. Between these two extremes are a general cutting task for which any sharp flake would suffice and a large dart point for killing deer. Chert is an excellent material for either task, but in the northern Kayenta region chert to make simple flakes for expedient cutting is far more ubiquitous than chert well suited for large dart points. The latter require rocks with properties beyond simply being able to fracture and produce sharp edges. Principal among these are adequate nodule size and lack of internal flaws. These requirements atomically raise the standards-bar and the lithic landscape of the northern Kayenta region appears correspondingly far more improvised. V.5.3 |
