4.3. Formations in the Upper Colca Valley

The volcanic terrain and the temperate lower valley in the Chivay area have largely conditioned human activity patterns in the region for the past 10,000 years. The local geological sequence will be summarized from text and maps from Palacios et al. (1993) the primary INGEMMET source for the region, as well as the ONERN (1973) geological study associated with the Majes Irrigation project, and the discussion will be supplemented with evidence from more recent specific studies in the region.


Figure 4-13 Rock groups in the Colca region (based on Palacios et al., 1993).

The Colca region is dominated by late Cretaceous sedimentary rocks overlain by Tertiary flows and tuffs of basaltic to rhyolitic composition. Some Jurassic sedimentary strata are exposed consisting of sedimentary and metasedimentary rocks. The region has continued to be volcanically active during the Pleistocene and Holocene epochs in the form of stratovolcanoes that ring the Colca valley as well as exogeneous andesitic domes and flows occurring in the Colca River valley itself.