The LCZ is located at lower elevations than is the UCZ, generally between 3820 and 3880 m.a.s.l. (Table 2.1). The zone was described by Albarracín-Jordan as follows:
This area is characterized by colluvial fans, which are intersected by the quebradas of the Upper Colluvial Zone (UCZ). These quebradas, however, are much wider in this area, and, during the rainy season, they become true streams, transporting water, sand, and mud.The soils of the colluvial fans are deep and fertile. ([Albarracín-Jordan 1999]: 4)Most of the vegetation present in the UCZ is present in the LCZ, as well. In addition, we see yawarilla (Aristida spp.), sanu-sanu (Ephedra americanus), and chillihua (Festuca dolichophylla) ([Albarracín-Jordan 1996a]: 13). The LCZ is the principal agricultural zone on the peninsula, and the full range of crops is planted. It is presumably for this reason, and for easy access to water, that the majority of archaeological sites are located in this zone. So too are the majority of contemporary residents of the peninsula.
Though Albarracín-Jordan does not mention this fact, it is also the case that the average clast size is smaller in the LCZ than in the UCZ. I believe this to reflect the fact that in actuality the LCZ is composed mostly of quaternary lacustrine deposits, and thus is entirely distinct geologically from the UCZ. This is made very clear by a published geological section of the Taraco Peninsula ([Argollo et al. 1996], Figure 3.7). This profile clearly shows terraces deposited by the paleolakes Tauca, Minchin, and Ballivian overlying the slopes of the Taraco Formation at depths of up to 20 meters. The maximum clast size of these lacustrine terrace deposits, which show evidence of wave action, is only about 6 cm ([Argollo et al. 1996]: 75), which is considerably smaller than the 20 cm clasts which occur in the Taraco Formation ([Argollo et al. 1996]: 69). Thus the difference between the UCZ and the LCZ is not that the latter represents colluvium derived from the former, as Albarracín-Jordan suggests. Rather, the UCZ represents eroded exposures of the Taraco Formation, while the LCZ represents relict paleolake terraces and related lacustrine deposits of more recent origin. Whatever the case, however, the two zones are clearly distinguishable.