[1] The Sierra Minera is part of the last eastern foothills of the Baetic mountain ranges, which arose in the Cenozoic during the so-called Alpine orogeny, due to the collision of the Mesomediterranean microplate with the Iberian plate.

Geologically, the Sierra Minera is composed of two superimposed tectonic units:[4] During the Late Miocene, the Campo de Cartagena suffered one of the most recent episodes of volcanism in the Iberian Peninsula.

About seven million years ago, numerous volcanic eruptions began to occur throughout the area, the remains of which are: the islands of the Mar Menor, Isla Grosa, El Carmolí or Cabezo Beaza.

In the 19th century, the exploitation of lead was resumed from the old slags, then from the secondary minerals (anglesite and cerussite) despised by the Romans, and finally from galena, obtaining also silver.

From the mineralogical point of view, the Sierra minera de Cartagena-La Unión has produced remarkable specimens of most of the exploited species, and other minerals without industrial value, but of scientific interest, such as greenalite, vivianite or ludlamite.

[8] The earliest archaeological evidence of mining in the southeast comes from the numerous Phoenician shipwrecks that attest to commercial exchanges of mineral products with the East from the 7th century B.C.

[11] According to some historians, such as the well-known archaeologist Adolf Schulten, the establishment of the Carthaginians in the southeast of the Iberian Peninsula and the foundation of the city of Qart Hadasht, today's Cartagena, in 227 B.C.

Adolf Schulten, Fontes Hispaniae Antiquae.With this silver would most probably have been produced the minting in the city of a well-known series of Carthaginian coins with the effigies of the Barca family found in Mazarrón and in other points of the Levant in the 19th century.

Diodorus of Sicily (Bibliotheca historica V, 35, 4–5).In 209 B.C., in the context of the Second Punic War, Scipio Africanus, motivated by the interest of taking control of the silver production of Cartagena, conquered the city of Qart Hadasht for the Roman Republic, renaming it Carthago Nova and granting it the status of municipium.

From this period comes the famous Cabezo Rajao mine, where a superficial vein of argentiferous galena was emptied, leaving a large crack in the mountain, the origin of its current etymology.

[23] The end of mining led to the rapid decline of the city of Carthago Nova, the abandonment of half of the urban area and the ruin of most of the buildings constructed in the Augustan period.

A few years later, in 1839, the very rich Jaroso vein was discovered in the Almagrera mountain range in Almería, which unleashed a genuine mining fever throughout southeastern Spain.

[27] With the wealth generated by the mining activity, a powerful bourgeoisie grew up in Cartagena, who invested their enormous fortunes in luxurious houses and palaces in the modernist style.

[28] At the beginning of the 20th century, this golden apogee of the mining sector in Cartagena began to decline suddenly due to the appearance of strong competitors in the international market (mainly the United States and Australia) with more efficient technology than that used by local companies.

This botanical wealth makes up one of the most important plant heritages in Europe and is mainly concentrated in the coastal mountain ranges of the Campo de Cartagena, where the humidity provided by the mists from the sea mitigates the aridity of the climate.All these species are organized in different ecosystems and habitats, many of them of great ecological value and extremely rare in Europe, which has led to the declaration of seven botanical micro-reserves in the mountains.

[38] The Cartagena cypress forests or Tetraclinis articulata, present in the Peña del Águila and Monte de las Cenizas, are particularly noteworthy in this aspect.

[41] These practices caused the disappearance of a very important extension of land that has now become a barren area and the loss of numerous habitats and species, such as the jara de Cartagena, a plant formerly described as abundant in the mining sierra, which was considered extinct until its rediscovery in 1983.

[42] However, the biggest problem came from the disposal of the enormous quantities of tailings or mining waste, which in the form of sludge were dumped by the Peñarroya company directly into the sea in the bay of Portmán.

Due to its geological and historical-industrial values, as well as the intense transformation of the landscape generated by the mining activity, the Sierra Minera has been declared a Good of Cultural Interest (BIC) by Decree of April 30, 2009 of the Governing Council of the Autonomous Community of the Region of Murcia, with the category of historical site.

[1] As far as environmental protection is concerned, in spite of the tremendous ecological impact generated by the mining works, the Cartagena-La Unión mountain range still conserves important natural values.

leases to private individuals are frequent, possibly because they do not give the public treasury sufficient yield and an accelerated manumission makes the available labor force fall alarmingly (...) At the beginning of the 3rd century A.C. the mines of Carthago Nova and its metallurgical installations are vestiges of a brilliant past.

The area became a center of labor attraction, converging on it a powerful flow that, coinciding with the depletion of the best deposits of Gádor and Almagrera, will arrive mainly by the roads of Almería.

At the end of this stage the sector was already in frank regression, giving rise to the closure of countless mines and a sharp population drain, perceptible in the loss of personnel in the municipality of La Unión.

The climax vegetal landscape of the Campo de Cartagena is a maquis dominated by mastic, palmetto, wild olive trees and mainly atochas (Chamaeropo humilis-Rhamnetum lycioidis).

The natural vegetation of maquis has been replaced by one of hawthorn (...) It has been the destructive action of man, with the overexploitation of forest resources and the clearing of uncultivated land that has determined the end of the natural regeneration capacity of these mountains (...) This process of deterioration culminates with the great increase in population during the 18th century, when the rupture occurs that brings with it the replacement of a landscape of maquis to one of hawthorn.

(...) Among the plants useful to man, only palm hearts and esparto grass remained in our mountains in the middle of the 19th century, dotted with small stands of pine trees with its maximum exponent in the Peña del Águila.

(...) At the moment, there is a debate on the possible urban development of the Portmán Bay area, a natural corridor containing some of the most strategic Tetraclinis patches in relation to the connection between the main populations of this species.

The coincidence of the main fires with the dates of protection of the natural spaces of the area and the beginning of the economic-urban reactivation of Portmán due to the regeneration of its bay, nowadays clogged with mining sediments, seem to suggest a causal relationship.

In the most recent fire at the end of August 2011, about 2800 individuals of Phoenician juniper were affected, which represents 34.1 % of its total population in Murcia, about half of which had already been burned less than twenty years ago.

One of the engines of Cartagena's industrial development left behind a serious ecological problem, with 50 square kilometers of crushed mountains and a bay —Portman Bay— that became the largest source of pollution in the Mediterranean.