## 4 Geological Characteristics of Rock Shelters  
### Morphology  
The general morphological characteristics of the six rock shelters studied are provided below. The main alteration products, whose mechanisms of formation are explained later, are schematically indicated:  
* The Cueva del Tajo de las Figuras is a rock shelter opening towards the south, 5.8 m in height, 4.2 m wide, and 8 m deep (Figure 1B). It is located on a vertical incision corresponding to a fault plane with an E-W direction (Figure 2A). It has alveolar structures formed by one centimetre to decimetre-width alveoli with a spherical to ellipsoidal section particularly located in the back wall and the ceiling of the shelter. Holes are used by animals (wasps and birds) for their nests. Patinas of reddish to blackish tones are abundant on the walls and ceiling. Whitish patinas on the external part of the shelter are also present. These stains are closely related to the colonisation of plants and the defecation of animals. The floor of the shelter has a smooth, polished, shining surface. Fallen rock flakes are abundant, particularly in the more external part of the shelter;The Cueva del Arco is a rock shelter with a domed roof and an overhanging rock ledge that has partially collapsed. Consequently, a large arch with an elliptical section has been formed at the entrance of the cavity (Figure 2B). Its approximate dimensions are 2.3 m in height, 10 m wide, and 7.5 m deep (Figure 1B). Alveolar surfaces throughout the stratification are abundant on the walls and ceiling. The alveoli are one centimetre in width and have an ellipsoidal shape. Both the walls and the ceiling and floor show patinas of reddish and orange tones and an abundant colony of fungus, lichens, and other plants. Remains of fallen rock flakes are numerous; Shelter 11 (Penas de Cabrera) is morphologically similar to the Cueva del Tajo de las Figuras, but not as deep, with approximate dimensions of 5 m in height, 4 m in width, and 2.5 m deep (Figure 1B). This shelter is orientated to the north and has developed on a practically vertical E-W fracture plane. Alveolar structures similar to those previously described can be seen on the ceiling and upper part of the walls of the shelter (Figure 2C). The floor is covered with a patina of an intense red colour, with bright and dark areas. The red tones of the floor appear to be related to the traces of Neolithic pictorial activity. A well-defined surface blackening can also be observed on walls and ceilings; Shelter 13 (Penas de Cabrera) faces the north according to fracture planes in a N100E direction and a dip of 50-60\({}^{\circ}\) S (Figure 2D), with the development of one meter-width fatone morphologies on its back wall (Figure 2E). This is a shelter with little depth (less than 3 m) and a maximum height of 8 m (Figure 1B). Honeycomb structures formed by alveoli of the order of one millimetre can be seen on the back wall of the shelter together with brownish orange patinas, fallen rock flakes, and white marks from the defecation of animals. Traces of biological communities, such us fungi or lichen, on the inner walls of the shelter are practically absent; Shelter 17 (Penas de Cabrera) is 2.5 m in height, 6 m wide, and 1.8 m maximum in depth (Figure 1B). It faces north and is located very near ground level, thus making a very clear ground-level ledge. This shelter is almost masked by abundant vegetation. Reddish patinas and signs of fallen flakes are very abundant. The lower part of the shelter, up to a height of 50 cm, does not show alteration patinas and is completely devoid of flakes (Figure 2F); Shelter 24 (Penas de Cabrera) faces west and is small (1.8 m high by 4 m wide and a maximum depth of 1.5 m) (Figure 1B). This shelter has a great development of alveolar morphologies in the interior, particularly towards the ceiling. Colonisation of fungi, lichens and other plants is abundant. The walls of the shelter have a very extensive blackish patina.