of animals available to be hunted. Regardless, the fact that many people gathered in one place to contribute to the rock art for such a long period shows a large cultural significance, or at least usefulness, to those who participated. Materials The binder used in the artwork is unknown, but the mineral pigments include iron oxides, producing reds and purples; kaolin, producing white; natrojarosite, producing yellow; manganese oxide (pyrolusite), producing black; and copper oxide, producing green. Haematite, goethite, green earth, quartz, and calcium oxalate have also been detected. Gypsum was used, which allowed the pigments to better adhere to the surface of the rock faces. Stylistic groups Specialists have categorized the art into four stylistic groups, as proposed by Carlos Gradin and adapted and modified by others: A, B, B1, and C, also known as Río Pinturas I, II, III, and IV, respectively. The first two groups were partly conceived to differentiate group A's dynamic depiction of guanacos from group B's static depiction of them. Stylistic group A Stylistic group A (also known as Río Pinturas I) is the art of the first hunter-gatherers who lived in the area. It is the oldest style in the cave, and can be traced back to around 7,300 BC. The style is naturalistic and dynamic, and encompasses polychrome, dynamic hunting scenes along with negative human hand motifs. The imagery takes advantage of the grooves and irregularities in the rock face itself to form part of the art. This is especially true in the use of these irregularities to represent the topography of the settings of the images, such as in the depiction of ravines. The hunters depicted in the scenes were likely long distance hunters, and the scenes often depicted ambush or surround tactics being used when hunting guanacos. Since 2010, this stylistic group has been further subdivided into five different sub-styles, or series, categorized by color/material. These series are classified as A1 (Ochre series), which is primarily made up of ochre and some red; A2 (Black series), which is predominantly black but also contains some dark purple; A3 (Red series) which primarily incorporates red; A4 (Purplish/Dark Red series), which uses purplish red and dark red; and A5 (White/Yellow series), which predominately uses the color white but also incorporates yellow-ochre. In terms of layering, A2 generally covers A1; A3 goes over A1 and A2; A4 goes over A3 and A2; and A5 is