The Middle Archaic Period, as with the preceding period, is still poorly understood in the region as very few highland sites containing stratified deposits have been studied from this period. In the Lake Titicaca Basin paleo-climatic evidence points to significant aridity, a lake level approximately 15m below the current stand, and high salinity in Lake Titicaca that is comparable to that of modern day Lake Poopó(Abbott, et al. 1997;Wirrmann and Mourguiart 1995). Human occupation during the Middle Archaic in the Lake Titicaca Basin was notably higher than in the preceding period, but research shows that settlement continued to occur in the upper reaches of the tributary rivers and not adjacent to the shores of the saline Lake Titicaca(Aldenderfer 1997;Klink 2005).
At the site of Asana on the western slope of the Andes, Aldenderfer(1998: 223)observed architectural features that suggest that a longer residential occupation of the site by entire coresidential groups was occurring in the latter part of the Middle Archaic Muruq'uta phase.One flake of obsidian from the Chivay source was found in the upper levels of theMuruq'uta phase (XTable 3-4X).This occupation dates to the Middle Archaic -Late Archaic transition as the flake was stratigraphically above a14Csample that dated to 6040 ± 90 bp (Beta-24634; 5210-4720 BCE).
At the rock shelter of Sumbay SU-3 obsidian was recovered from excavation levels that date to as far back as the transition between the Middle and Late Archaic (SectionX3.4.3X).
Relatively little is known about the Middle Archaic in the south-central Andean highlands. Elsewhere in the south-central Andes, archaeologists have noted an absence of settlement during the mid-Holocene timeframe corresponding to the Middle and Late Archaic Periods. In the dry and salt puna areas of northern Chile, and along the south coast of Peru, a significant decline or absence of mid-Holocene sites has led investigators to refer to this period as the silencio arqueológico(Nuñez, et al. 2002;Núñez and Santoro 1988;Sandweiss 2003;Sandweiss, et al. 1998). This designation apparently does not apply to the Titicaca Basin or to the sierra areas of the Osmore drainage where no Middle Archaic occupation hiatus has been observed.
With gradual population increases and adaptation to the puna, social networks extending across the altiplano and connecting communities and their resources residing in lower elevations with puna dwellers, were probably beginning to take form. Exchange of resources, including obsidian, between neighboring groups may have been in the context of both maintaining access to resources and risk reduction. From a subsistence perspective, Spielmann (1986: 281) describes these as buffering, a means of alleviating period food shortages by physically accessing them directly in neighboring areas, and mutualism,where complementary foods that are procured or produced are exchanged on a regular basis. Another likely context for obsidian distribution during the Archaic Period is at periodic aggregations. Seasonal aggregations have been well-documented among foragers living in low population densities, where gatherings are the occasion for trade, consumption of surplus food, encountering mates, and the maintenance of social ties and ceremonial obligations (Birdsell 1970: 120;Steward 1938). If analogous gatherings occurred among early foragers in the south-central Andes it have would created an excellent context for the distribution of raw materials, particularly a highly visible material like obsidian that was irregularly available in the landscape.