The Natural Park is rich in quartzite and gneiss, dating from over 300 million years ago. The Sierra Almijara has one of Spain's most important areas of dolomitic marble, which is apparent from the grey and white tones produced by surface erosion. In contrast, Sierra Tejeda is mainly limestone from the Eocene period, which has weathered to leave steep-sided ravines and plunging cliff faces. This erosion has also occurred underground, resulting in a high concentration of caves, the most famous of which is that of Nerja. Others are found on the Maroma and close to the village of Canillas de Aceituno.