It is certain that the olivine basalt (RMT 61 and 65) that appears on the Taraco Peninsula in the Middle Formative is of exotic origin. There is no such material present in either the Taraco or the Kollu Kollu formations (see section 2.1). Although its source cannot at present be determined with certainty, I would like to venture an educated guess. The only documented quarries of this raw material type are located in the vicinity of Chucuito, south of Puno on the western side of Lake Titicaca. These quarries were discovered by Kirk Frye in his dissertation research. The nearby sites of Incatunahuiri and Dos Suches are both covered with literally hundreds of tons of hoes, debitage and manufacture failures of this material ([Frye and Steadman 2001]). I have visited these sites, and can attest that the stone there is visually identical to the RMT 61 and 65 objects from the Taraco Peninsula and other areas.
Further evidence is provided by Steadman. In her excavations at Camata, located somewhat south of Chucuito, and possibly within the Middle Formative political radius of Incatunahuiri, she finds that hoes of this material - which she terms ``gray andesite'' - first began to appear in limited quantities in the Early Qaluyu 2 phase (1050-850 B.C.) ([Steadman 1995]: 32). This ``gray andesite'' became progressively more popular through time at Camata, finally accounting for almost 90% of the lithic sample by the Pucara 2 phase (100 B.C. - 100 A.D.). This process began in the Middle Formative, in the Late Qaluyu 1 phase (850-650 B.C.), roughly contemporary with the earlier part of Late Chiripa. Steadman interprets the increased hoe production at Camata in the Middle Formative as reflecting agricultural intensification and raised field construction ([Steadman 1995]: 41). Given the data from the southern basin, however, I believe this intensified hoe production reflects instead production for export to other areas of the Titicaca Basin, as part of a regional exchange system.
Frye and Steadman ([Frye and Steadman 2001]) argue that Incatunahuiri was the production center for these hoes, and an important hub of an exchange network extending across the entire Titicaca Basin. Geochemical characterization of hoes from throughout the basin will be necessary before this hypothesis can be proven conclusively, and I plan to undertake such a study in the very near future. For the moment, however, I will provisionally accept Incatunahuiri as the source for the olivine basalt on the Taraco Peninsula sites.