The Cerro del Hierro, one of the best known and most frequently visited areas of the Sierra Norte Natural Park, is an old open-cast mining site located between the municipalities of San Nicolás del Puerto and Constantina, the southern part of the park belonging to the latter. The beginning of its mining goes back to the Roman period and it was in operation, although in a discontinuous way, until 1985. The bags of iron ore were extracted from the mine between the crests of an ancient karst area, revealing a unique landscape of limestone forms in which a highly diverse Mediterranean vegetation has subsequently developed, due to the varying conditions found in this unique spot.
In the Cerro del Hierro both natural forces and human factors have united to create a spectacular landscape. The Cambrian limestones of the area were subjected to the action of external weather conditions, such as rain and wind, causing their karstic formation, which was hidden under layers of iron-bearing materials. In more recent times, man exploited these iron deposits, in the form of oxides, accumulated on the limestone. This mining of materials exposed the paleokarst formation, giving rise to the landscape that can be seen today.
Although it is a rocky place, the inner part of the canyons and the low areas of the terrain are occupied by a highly diverse vegetation, due to the varying conditions created by the unusual relief. In the sunny areas, holm oaks and wild olive trees predominate, while in the shady areas, cork oaks and Portuguese oaks are common, along with some Pyrenean oaks, a species that is native to the Seville’s Sierra Morena. In the interior of the canyons, the high level of moisture promotes the development of species such as fig and wild cherry trees. There is a wide variety of shrub species, and various species of ferns and lichens live in the narrower and more humid canyons.
In the northern part of the area belonging to San Nicolás del Puerto you can still find the old mining town where the mine workers lived, which is now a district of this municipality, also called Cerro del Hierro.
The Cerro del Hierro is highly frequented by the public, and educational, sports and leisure activities are carried out there. It offers the possibility of hiking, climbing, caving and mountain biking, as well as botanical, geological and birdwatching tours.
On 1 October 2003, the Junta de Andalucía declared it a Natural Monument of mixed character due to its geological, eco-cultural and biotic values.