The geological substrate in Rajadell is made of sedimentary rocks sourced from mud, sand and gravel that settled down in a continental area -a wide flooding plain- 34 million years ago between the Eocene (older) and Oligocene (more modern), two epochs from the Tertiary. Therefore, it contains clays, sandstones and conglomerates usually reddish coloured after their oxidised iron content.
The differential erosion on those materials has resulted in a tabular relief of high slopes and flat tops made of a much more consistent rock layer (greystone or conglomerate) than the clay beneath.
Subsequent to the erosion of the clay layer beneath, the rocky edges of those plains break and release big blocks that slip down in the slope. The blocks of rocks in the landscape are known in geology as a chaos. The most outstanding chaos of sandstone and conglomerate rocks in Rajadell are the chaos of cal Miralles that’s displayed in the photo and the chaos of El Puig, one quilometer east-northeast, by the road C-25.
[photo Florenci Vallès].