Located on the north face of Sierra Bermeja, these natural cavities were used to grind gold and silver ores in the early 18th century, according to records. However, there is no clear evidence of such use.

The Morteretes are rather circular cavities that form in the Sierra Bermeja rivers and streams and have traditionally been mentioned in the 18th and 19th centuries as spots for crushing the ore, mainly gold and silver from the mines around. Morteretes can be found on the north face on the way to Genalguacil (Garganta del Algarrobo and Arroyo Cueva de Baque) and on the south face towards Estepona and Casares (Arroyo del Infierno, Guadalobón River, Arroyo de la Cala, Garganta de las Minas). Sierra Bermeja also abounds in gold, albeit in microscopic form. Nonetheless, it is unlikely that previous societies, which had little technological development, would actually use these structures for the purposes traditionally attributed to them.