The implementation of high-resolution thin section mosaics was applied to characterize the volcaniclastic reservoir of the Las Cabras Formation of the Cuyana Basin, based on the interpretation of the processes that modified the porosity and permeability conditions. The deposits of Las Cabras Formation are filling the halfgrabens formed during the first extensional stage of the Cuyana Basin; and they are constituted by different volcaniclastic events, which generated predominantly ignimbritic deposits, characterized by containing crystalloclasts, volcanic lithics and vitroclasts. These deposits have intragranular, intracrystalline and interparticle porosity, the latter occurring in the vitreous matrix. Some of these intervals are palagonitized with their porosity obliterated. Detailed petrographic compositional and textural analysis serves to characterize the pore system of the reservoir rocks. Measurements of the components and of the pores were made from point counting and image processing of the thin section mosaics. From the results, similarities and differences of the different intervals of Las Cabras Formation are recognized. The deposits of Las Cabras Formation due to their predominantly volcaniclastic origin, were deposited in a wide range of temperatures. The initial temperature and fluids involved could influence the generation of some dissolution and cementation processes. Being able to define the origin of the elements associated with dissolution and cementation, as a product of deuteric, hydrothermal or diagenetic processes, is of vital importance for understanding the spatial distribution of the reservoir facies.