A number of models have been presented for regional interaction and exchange in the south-central Andes (Bandy 2005;Browman 1974;Browman 1980;Browman 1981;Burger and Asaro 1978: 68-70;Dillehay and Nuñez 1988;Nuñez and Dillehay 1995 ;Stanish 2003). This study evaluates a selection of these models at the Chivay obsidian source in the highlands of Arequipa. Renfrew explored various configurations for interaction and his "exchange modes" are reviewed above in Chapter 2 (Figure 2-2). These models will be discussed with respect to activity at the Chivay source area and material expectations for what may result from each model in the vicinity of the obsidian source. It should be noted that due to the extremely thin cortex on many Chivay obsidian nodules, decortication is not a consistently useful measure of reduction level or labor investment, but none-the-less the Upper Colca lab analysis sought to measure percentage of remaining cortex on flaked stone artifacts. When the geological cortex is of the extremely thin variety, it is sometimes left on the face of tools and it does not pose an obstacle to knapping. As cortical flakes from obsidian with a thin cortex are often smooth, and can be equally sharp, one should therefore not assume that nodules will be decorticated in the quarry area.
A number of modes of procurement are explored here, but these acquisition and exchange modes are not mutually exclusive either in time or space. That is, a variety of processes were likely to have been occurring simultaneously. For example, a independent caravan have transported an obsidian nodule to a site in the Ilave river valley, and then obsidian nodule may have been transmitted through down-the-line trade from the Ilave area to the Tiwanaku area. These models, therefore, will focus specifically on procurement and initial transport from the Chivay source because that is where more direct material correlates for these different models can be expected.