The southern margin of the Santa Cruz river basin
At low elevations located in the upper river basin, human occupations are discontinuous until about 5.300 years ago, when the longest period of humidity identified in the area begins, according to paleoenvironmental studies.
Shortly after, the first occupations were recorded in the Sierra Baguales, at the Cerro Verlika 1 site, at approximately 1,100 meters above sea level.
About 4.300 years ago, after a volcanic ash was deposited in the area which, according to Ch. Stern's analysis, came from the Aguilera volcano (Chile), human burials were found. Individuals of different ages have been found - adults and young people or children - who have been deposited over a period of approximately 200 years in structures excavated within the rock shelter called Río Bote 1, which were covered with rocks. At the time when these burials were found, the Bote river had eroded a large part of the site and the remains it contained -including human ones-, were at risk due to natural and cultural factors.
The analysis conducted by T. Montenegro revealed that the bodies were likely wrapped in painted leather, as suggested by the presence of pigment on the bone remains and its absence in the surrounding sediments. In some cases, remains of lithic and bone tools were found in close proximity, which may have been deposited alongside the bodies. However, since the excavation of the structures for body deposition reached older layers containing artifacts and food remains, it is difficult in many instances to determine whether these items were deposited with the bodies or if they originated from earlier occupations. Similar burials in structures dug into rock shelters were also found further south, in the volcanic field of Pali Aike and near Última Esperanza, in Chile. This suggests the existence of shared customs between people living in the upper basin of the Santa Cruz river and those farther south, more than 250 km away, between 4.200 and 4.000 years ago, which could indicate either shared cultural practices among different groups or their movements over time.
According to the genetic studies carried out by Moraga and Galimany, the analyzed individuals recovered at the Río Bote 1 site were related. The maternal lineage to which they belong is striking given its low frequency in current aboriginal populations of central-southern Patagonia and in other individuals from early sites in Patagonia. In one of the cases, the analyses corresponding to the paternal line show the presence of a lineage not represented until now in Patagonia.
On the other hand, about 4.300 years ago a new method of knapping rocks began to be used in the upper basin of the Santa Cruz river, which is the recurrent Levallois centripetal method, a variation of the Levallois technique (see Lithics in Research Lines). We do not know if the use of this new flintknapping method can be related to the improvement of the climate and a new way of using the area -which brought with it a technological variation- or to the entry of new human groups into the area, which is possible given the low population densities in South Patagonia. This same flintknapping method is present further south, in the area of Cerro Castillo, about 90 km away in a straight line, as shown by the analysis of M. Langlais and F. Morello, and it has also been identified further south, both in continental and insular Patagonia. However, it has not been found so far north of the Santa Cruz river basin, in central Patagonia.
The existence of similarities in technology and burial methods between the Santa Cruz River basin and spaces located further south, and the lack of these to the north of this river, suggests that it is likely that between 4.300 and 3.900 years ago different cultural groups inhabited the north and south of the basin, something which should continue to be studied. This does not mean that there was no occasional interaction between them.
Just over 3.300 years ago we find the first occupations in a rock shelter in the forest, west of Lago Roca and also, according to the dating obtained by F. Carballo Marina, the first evidence of human use of the dunes, on the coast of Lago Argentino.
Occupations on sand dunes became more frequent around 2.500 years ago, during a period of climatic fluctuations between wetter and drier phases. These were generally brief occupations. In one case (Alice 1), laminar blades obtained using a systematic technique were identified (see Lithics in Research Lines), while in other cases (Laguna Nimez), the recurrent Levallois centripetal flintknapping method was identified.
This period of climatic fluctuations corresponds to the first evidence of utilization of the recurrent Levallois centripetal flintknapping method along the coast, which was identified in two sites located in canyons in the plateaus, with evidence of shell consumption (figure). The reason for the presence of this flintknapping method in the coast remains unclear; it may reflect a method shared by different human groups south of the river, or the result of human movements due to environmental fluctuations in the upper river basin. This method has also been found in the middle course of the basin as part of archaeological work related to the recovery of archaeological remains affected by the future construction of dams; there are not still dates for these findings.
Throughout human occupations in this area, the main prey exploited is the guanaco, although some changes in its use have been found, which in some cases may have been related to identified climatic variations (see Fauna in Research Lines).
Around 800 years ago, there was a prolonged period of aridity. Sites corresponding to this period are scarce. Subsequently, new human groups are present in this area, differing both culturally and genetically from the previous ones. Cultural changes are evident in their technology, the way they buried their dead – the use of rock structures known as chenques in Patagonia began – and in the use of pigments in these burials -as shown in the analysis carried out by Montenegro and co-authors-. Genetic studies by Moraga and Galimany also showed that the new human populations were present south of the river shortly before the Europeans.
Little is known about the years prior to contact. The dates we obtained from a dune in the middle course of the river show that these areas continued to be used. On the other hand, the circular rock structures located south of Lago Argentino, dated through lichens by Borrazzo and Borrero, likely correspond to this period. Additionally, structures consisting of concentric circles formed by a single row of stones have been identified both in the middle course of the river and south of lago Argentino. The existence of these different types of structures suggests that, by this time, the ancient inhabitants of the area were utilizing open spaces and construction rock structures, meaning they were modifying these spaces for future use (see Rock Concentric Circles in Lines of Evidence).
It should also be noted that, in connection with the archaeological works related to the planned construction of dams in the Santa Cruz river, pottery fragments have recently been recovered in dunes both in the upper and middle basin of the river, a technology which is new south of the river. Unfortunately, we still lack chronologies for these findings although, taking into account the dates obtained in the north of the river and the probable dispersion of this technology from north to south -as other researchers have suggested-, it is likely that it corresponds to this latter period.
On the other hand, although the results of the research suggest that different human groups existed to the north and south of the river during most of the last 4000 years, there were interactions between them, as indicated by the presence of raw materials from one of these areas in the other (for example, black obsidian).
In addition and regarding rock art motifs and techniques, during surveys and rescue work carried out in relation to the planned construction of the Néstor Kirchner dam (formerly Cóndor Cliff), rock engravings were identified at the archaeological site of La Porfiada, south of the river. They resemble those found on the northern side of the basin, with the presence of reticulated patterns, human footprints, and tridactyls. Engraved human footprints have not yet been identified further south. The similarities and differences with other spaces in the basin are currently being studied in greater depth.
In La Porfiada there are also hand stencils that are common north of the Santa Cruz river and that, south of the basin, are only present in the archaeological localities of Walichu-Punta Bonita, in Lago Argentino.
The similarities between the motifs and techniques identified at La Porfiada and those found in the canyons on the northern side of the Santa Cruz river basin could suggest the mobility of human populations. These routes may have varied over time, which could explain some of the similarities and differences observed in the flintknapping artifacts and rock art, a topic that requires further study. The GIS analyses conducted have focused on understanding the most probable circulation pathways between these areas.
Finally, the rescues in relation to the planned construction of dams in the Santa Cruz river have allowed us to identify the continuity in the use of flintknapping techniques in historical times, as indicated by the presence of endscrapers made on industrial glass. These findings complement those made by researchers such as J. B. Belardi and co-authors south of our study area, near the Aonikenk (Tehuelche) Reserve of Camusu Aike. As these authors mention, these findings show the disarticulation of the populations that occupied these spaces with European and criollo presence.