A record etched in stone
Located 28 kilometers south of San Rafael, the Gruta del Indio is a basalt rock shelter that holds a multi-layered record of human and animal activity in the southern Mendoza Province. The site sits at approximately 660 meters above sea level and contains a large deposit of archaeological evidence stratified into four distinct periods. Archaeological work, which began in 1956 under Humberto Antonio Lagiglia, has revealed a long history of occupation and use.
The deepest and oldest layer, Atuel IV, contains remnants of charcoal and evidence of fire pits, alongside the remains of megafauna. Radiocarbon dating of charcoal and dung samples from this layer suggests a period of overlapping animal and potential human presence between 12,880 and 12,000 years ago. This makes Gruta del Indio one of the few sites in South America with coexisting evidence of humans and large extinct Pleistocene animals, such as giant ground sloths. The sediment composition in the shelter is primarily composed of detrital grains, including volcanic lithoclasts and vitroclasts, indicating a local origin from the erosion of the basalt shelter itself mixed with fluvial and pyroclastic materials. The low mineralogical maturity of these sediments suggests that a dry, cold climate prevailed for much of the site's history.
The painted narrative
The most recent archaeological stage, Atuel I, is defined by the pictographs that adorn the rock shelter's walls. These paintings represent a long tradition of rock art, with some figures depicting historical events such as the arrival of Spanish soldiers. The art is varied, featuring zoomorphic and geometric figures. The color palette is dominated by different shades of red, with some use of yellow, white, and black.
The paintings show a shift in subsistence strategies over millennia. Earlier depictions show guanacos and rheas, animals central to the hunting practices of early inhabitants. Later images include representations that suggest an incorporation of agriculture. Abstract geometric designs are also prominent. Some researchers propose these patterns could be early forms of cartography, mapping the local terrain, water sources, or celestial events. The study of such art often involves stylistic comparisons to other sites with dateable materials to establish a relative timeline. While direct dating of pictographs can be difficult, methods like Accelerator Mass Spectrometry (AMS) can be used on pigments containing organic binders like charcoal.