Rock Structures
It is very common to find accumulations of rocks left by the ancient inhabitants of Patagonia. Archaeologists call them structures, and their shapes and functions vary.
To understand why they were built, we look at their shape, where they are located, where the rocks they used were obtained, and what other objects the old inhabitants left inside or near them.
It is important to be able to differentiate structures built by humans from other types of accumulations that can occur naturally, so we study the geological and geomorphological processes that can form natural accumulations, in addition to working with specialists in these disciplines.
Within our areas of study, we find different types of structures:
A - Rock circles
These circular or sub-circular structures were sometimes used to cover human burials, in which case they are called chenques. In our study area they are found in elevated locations and are up to 790 years old. Only two were studied because they were open and at risk due to cultural and natural factors.
There are rock circles similar to the chenques, but without burial sites. Their exact function is unknown, but they may be territorial markers, pre-prepared graves, or have some other use that we do not know about.
Finally, there are other accumulations of similar rocks in the region, but it cannot be defined if they are chenques or not because they were not opened.
It is very common to find this type of structures in the Santa Cruz river basin.
B - Rock circumferences
These structures are built forming concentric circles with a single row of rocks; they may contain small accumulations of rocks in the centre and, sometimes, rocks between the different circles. They are more difficult to see than the previous ones, because they do not stand out as much on the ground. Some have been found south of the Santa Cruz river. They have been known since 1934 when the researcher Milcíades Alejo Vignati excavated one of them and found a burial at great depth.
The other two recently found structures were built on glacial deposits, so it is unlikely that there are burials beneath them.
These structures are another example of those that can be found in the Santa Cruz river basin.
C - Semicircular or subcircular structures
They are open structures of different shapes, built from several rows of rocks. Their possible uses include:
- Processing sites
- Hunting places
- Bases for shelters
They have been recorded both south of the Deseado Massif and north of the upper basin of the Santa Cruz river.
They are located on hills near lagoons, with or without direct visibility of them and, in some cases, are linked to the control of the circulation of the preys.
Visibility analyses are useful for evaluating how they are used. See the section Visible Basin Models in Spatial Analysis (GIS) in Research Lines for more information.
These types of rock structures appear most commonly in the Chico river basin.
D – Other forms of rock structures in historical times
For historical moments different types of accumulations can be found. Only some of them resemble those used previously.
Some of the historical structures that can be found in Patagonia are:
- The stone corrals.
- The piles of rocks near houses or outposts, used for orientation, especially during times of snowfall.
- Those arranged in a linear fashion for the construction of fences.
- Those used by explorers as reference points.
How do we know how old it is?
There are different ways to know when a structure was built:
- The most direct way is by doing radiocarbon analysis of organic materials associated with them.
- An alternative method is, for example, lichenometry. It helps us todetermine how long a lichen has been growing on a rock. By knowing the growth rate of a particular lichen (Rhizocarpon) and measuring its diameter, and then comparing those measurements against known growth rates, we can estimate the minimum time that has passed since the rocks in a structure were arranged in a particular way. It is not an exact dating method, but it is very useful when there is no other way to determine the age of the structures.
- Finally, when these methods cannot be used, the materials recovered from them can help us to approximate their age.