The range of Obac, mainly in the municipality of Mura, has many shelters (in Catalan, balmes). The best known are those that are occupied by the most elaborate constructions, specifically the Puig de la Balma that shelters a large medieval house and the Balmes Roges that covers a set of vats of wine; but there are many more, although not with such remarkable buildings.
Near the spring of Rector and the stream of Estenalles, in Mura, there is the shelter or balma del Sastricó. A low wall closes it at its deepest part. Facing south, the place is very comfortable on winter days.
Like most of the shelters in this area, the one of Sastricó results from differential erosion in a slope leaving a layer of hard conglomerate rock peeking out as a peaked cap over clay layers that are more deeply eroded. As a result of this origin, shelters are usually longer than deep. The presence of shelters with a conglomerate roof, such as that of the Sastricó, displays the resistance of the conglomerate to erosion and explains why the reliefs of the Obac and Montserrat mountain ranges are maintained, while the river network has deepened and drained through the Llobregat river the land between these two ranges.
[photos Montserrat Porta and Jordi Badia]