A number of the lag gravel deposits encountered in Blocks 4 and 5 of the survey are Ob2 material. Accordingly, obsidian artifacts from these blocks are higher in heterogeneities, indicating that there was a utility for this type of obsidian despite the imperfect matrix of the material. Investigating the distribution of Ob1 and Ob2 material across all obsidian artifacts (primarily flakes) shows that the Ob2 make up approximately one half of the obsidian artifacts even in Block 3 some distance from the Maymeja zone where Ob1 was observed in situ.

The mean size of Ob1 flakes is notably smaller, which suggests that more advanced reduction was occurring on the Ob1 material. There may be some size bias occurring with observations of heterogeneities because small flakes struck from Ob2 nodule will often appear relatively homogenous and clear if few bubbles or particles are included in the glass in that portion of the flake.

Table 6-11. Obsidian: mean sizes of complete Ob1 and Ob2 artifacts, by Survey Block.

These data, show patterns in terms of the mean length and weight differences between Ob1 and Ob2 artifacts. In all blocks, Ob1 artifacts are on average lighter than their Ob2 counterparts except for in Block 3. Furthermore, in most blocks the mean lengths of Ob1 and Ob2 material are very close but as the weights are different and therefore width or thickness must vary between Ob1 and Ob2 material. Further investigation of the metric data shows that, indeed, Ob1 artifacts have narrower and thinner medial measures, on average, than do Ob2 artifacts except for in Block 3 where Ob2 materials are thinner.

It appears that throughout the study region, Ob1 materials were preferentially knapped into artifacts that were narrower and thinner, but not necessarily shorter, than the Ob2 materials except for in Block 3. Ob2 material was much more common in Block 3, as will be discussed below, and it appears to have been used for more immediate butchering needs rather than for production of bifacial tools, a pattern that is consistent with the later date of the Callalli occupation. There is also a possibility of size bias where smaller Ob2 flakes are classified as Ob1 because no heterogeneities were evident in that particular small flake.