The Comarca Minera Geopark is located in the center-south of the Mexican state of Hidalgo. It extends over nine municipalities: Atotonilco el Grande, Epazoyucan, Huasca de Ocampo, Mineral del Chico, Mineral de la Reforma, Mineral del Monte, Omitlán de Juárez, Pachuca de Soto and Singuilucan. These municipalities are articulated by a network of 31 geosites, elected because they express the geological history of the territory and highlight the relationship between mining and metallurgy, and the historical spaces and cultural development of the region. In addition, they are important for science and education and, mostly, have a significant landscape value.
Geology
The Pachuca and Las Nevajas mountain ranges constitute the most important physiographic element of the Comarca Minera, with maximum altitudes in the Peña de las Ventanas (3090 m) and in the Cerro de las Navajas (3212 m), respectively. This orographic set has a northwest–southeast general orientation, and separates the area of the Sierra Baja and Barranca de Metztitlán (at north of the mountain ranges), with altitudes of ~ 1300–2000 m, from the northern end of the Mexico Basin (at south of the mountain ranges), with an altitude of ~ 2200–2400 m. The huge geodiversity of the park, appreciable in its geosites, is due to the fact that two physiographic provinces converge in the area, the Sierra Madre Oriental and the Transmexican Volcanic Belt, as well as two magmatic provinces, one related to the Transmexican Volcanic Belt and the other related to the volcanism of the Sierra Madre Occidental.
The Comarca Minera is characterized by an outstanding geopatrimony, which includes at least five geological (and cultural elements related to geology) that can be considered of international relevance:
The epithermal system (Ag-Au) of Pachuca-Mineral del Monte, one of the largest in the world; its historical production represents 6% of the silver produced globally during the last five centuries. The type locality, in the Cerro de San Cristóbal de Pachuca geosite, of tridymite and cristobalite, minerals discovered by Gerhard vom Rath in the years 1868 and 1887, respectively. The basalts with columnar jointing of Santa María Regla, Huasca de Ocampo, popularly known as the "prismas basálticos" (basaltic prisms), described and drawn by Alexander von Humboldt in 1803; they are generally considered the longest in the world (they reach 40 m in length). The mining industrial heritage, which includes haciendas de beneficio from the colonial era, as well as various mining works, among which those from the English mining period (mid-19th century), with splendid examples of Cornish-type machine houses, stand out. The Cerro de las Navajas, main point of exploitation and supply of obsidian for Mesoamerica, and exceptional site where obsidian in its golden and green varieties can be found.
Cretaceous
The oldest rocks in the geopark are limestones and shales of marine origin, of Cretaceous age, which are found in the northeastern portion of the territory and outcrop at the bottom of the Barranca de Metztitlán. It can be seen in the geosites:
Barranca de Aguacatitla Aguas termales de Amajac
Paleogene During this period, the belt of folds and ridges was formed, geographically known as Sierra Madre Oriental, through a compressive process that thickened and shortened the crust and raised the previously formed rocks in the sea to their current position. Towards the end of this period began the volcanism related to the subduction of the western Mexico. In the northwest sector of the geopark there are deformation structures, mainly asymmetric or even lying folds, of NNO-SSE direction, which can be seen in the geosites:
Barranca de Aguacatitla Aguas termales de Amajac
The volcanic rocks from the Oligocene are found in:
Depósitos tobáceos de Cubitos Mirador Cerro del Lobo
Miocene The magmatism initiated at the end of the Paleogene until the Middle Miocene, and it was responsible for large volumes of silicic volcanic rocks that constitute one of the most southeastern manifestations of the igneous province of the Sierra Madre Occidental. Associated with these rocks the epithermal mineral deposits of silver were formed, with an early Miocene age in the case of Pachuca-Real del Monte deposits, and a somewhat more recent (late Miocene) for those of Mineral del Chico.
Rhyolitic tuffs of the Tezoantla and Cerezo formations as well as rhyolitic and dacitic porphyry can be seen in the geosites:
Peña Las Monjas Peña del Cuervo Las Ventanas Depósitos Volcánicos de El Chico
The mineralization of late Miocene can be seen in:
Obras Mineras El Milagro
Pliocene The style and composition of volcanism changes due to the subhorizontal subduction of the Cocos Plate under the North American Plate, and resulted in the configuration of the Transmexican Volcanic Belt, which is still active today. Examples of volcanic rocks from the Pliocene are found in:
Cerro de San Cristóbal (in the homonymous formation) Peña del Diablo y Peña del Comal
Fossiliferous lacustrine sediments (with remains of plants and fish) are also from the Pliocene and it can be found in:
Aguas termales de Amajac
Pleistocene
The volcanism of the Trans-Mexican Volcanic Belt is responsible for the volcanic stream of the geosite:
Prismas basálticos (dated in 2.58 Myr)
and of the monogenetic volcanoes of Singuilucan, appreciable in the geosite:
Estructuras volcánicas de la Paila
Holocene Regarding the exploitation of natural resources, in the geopark and throughout the continent, the greatest change was triggered by the meeting between the Old and the New World; in the pre-Columbian era, obsidian was intensely exploited and, after the conquest, mining was concentrated on precious metals.
As a manifestation of the active geological phenomena, at the northwest of the geopark there is the geothermal site (and geosite) of:
Aguas termales de Amajac (hot springs spa)
Geopark geosites
The geopark consists of 31 geosites of geological, biological and cultural interest:
<li>Aguas termales de Amajac <li>Barranca de Aguacatitla <li>Cantera de Tezoantla <li>Cerro de las Navajas <li>Cerro de San Cristóbal <li>Cristo Rey <li>Depósitos tobáceos de Cubitos <li>Depósitos volcánicos de El Chico <li>Estructuras volcánicas de La Paila <li>Ex-Convento de San Agustín <li>Ex-Convento de San Andrés Apóstol <li>Ex-Hacienda La Purísima <li>Mirador Cerro del Lobo <li>Mirador Las Ventanas <li>Museo del Paste <li>Museo de la Mineralogía <li>Obras mineras El Milagro <li>Panteón Inglés <li>Parque Estatal Bosque el Hiloche <li>Peña del Aire <li>Peña del Cuervo <li>Peña del Diablo y Piedra del Comal
<li>Peñas Cargadas <li>Peñas Las Monjas <li>Presa El Cedral <li>Presa San Antonio <li>Prismas basálticos <li>Reloj Monumental <li>Reserva de la Biósfera de la Barranca de Metztitlán <li>San Miguel Regla <li>Traquita El Guajolote
Flora and fauna
Flora Favored by its physiography of contrasts, reflecting its geological complexity, the territory of the Comarca Minera has numerous biomes that alternate with agricultural and urban areas, supporting a very diverse fauna. In the highest areas (altitudes above 2600 m), with a temperate and cold-temperate climate, there are oyamel forests (Abies religiosa), whose best preservation zone is the Parque Nacional El Chico. The mountainous areas of lower altitude, especially the Las Navajas mountain range and the northern slope of the Pachuca mountain range, are covered by pine forests and mixed pine-oak forests. The diversity of pine species is huge; among which the patula pine (Pinus patula), the Hartweg's pine (Pinus hartwegii) and the teocote (Pinus teocote), while the most representative of the oaks is the netleaf oak (Quercus rugosa). In the sunniest slopes of the Pachuca mountain range and at altitudes below 2000 m, at the north end of the geopark xeric shrublands can be found with abundant cactus such as bilberry cactus (Myrtillocactus geometrizans), several species of biznaga (Mammillaria magnimamma, Echinofossulocactus crispatus) and nopal (Opuntia streptacantha, O. tomentosa, O. robusta), cane cholla (Cylindropuntia imbricata) and Mexican fencepost cactus (Marginatocereus marginatus), also several species of agave (Agave horrida, A. triangularis), highlighting the pulquero agave (Agave salmiana) for its use for traditional pulque production.
Fauna The variety and alternation of natural and agricultural ecosystems supports an important diversity of birds and reptiles. Among the first, the following species stand out for being easily observable: scarlet flycatcher (Pyrocephalus rubinus), black phoebe (Sayornis nigricans), red warbler (Cardellina rubra), yellow-rumped warbler (Setophaga coronata), house finch (Haemorhous mexicanus), lesser goldfinch (Spinus psaltria), yellow-eyed junco (Junco phaeonotus), black-headed grosbeak (Pheucticus melanocephalus), curve-billed thrasher (Toxostoma curvirostre), broad-billed hummingbird (Cynanthus latirostris), white-eared hummingbird (Hylocharis leucotis), Rivoli's hummingbird (Eugenes fulgens), blue-throated mountaingem (Lampornis clemenciae), Lucifer sheartail (Calothorax lucifer), ladder-backed woodpecker (Dryobates scalaris), golden-fronted woodpecker (Melanerpes aurifrons), acorn woodpecker (Melanerpes formicivorus), black-vented oriole (Icterus wagleri), bullock's oriole (Icterus bullockii), Steller's jay (Cyanocitta stelleri) and green kingfisher (Chloroceryle americana). As for reptiles, more than 30 species have been identified; the more relevant, due to their emblematic character and for being listed as threatened (NOM-059-SEMARNAT-2010), is the Mexican plateau horned lizard (Phrynosoma orbiculare). Among mammals, the rock squirrel (Otospermophilus variegatus), Mexican gray squirrel (Sciurus aureogaster), ring-tailed cat (Bassariscus astutus), North American opossum (Didelphis virginiana) and eastern cottontail (Sylvilagus floridanus) are regularly observed. More elusive, they also inhabit the geopark: white-tailed deer (Odocoileus virginianus), southern pocket gopher (Thomomys umbrinus), coyote (Canis latrans) and the gray fox (Urocyon cinereoargenteus). Also various bats species (Leptonycteris nivalis, Desmodus rotundus, Choeronycteris mexicana, Dermanura azteca). This biodiversity also includes 10 species of amphibians.
Protected natural areas
National
Parque Nacional El Chico Reserva de la Biósfera de la Barranca de Metztitlán
State-owned
Parque Ecológico Cubitos Parque Estatal Bosque el Hiloche Zona de Preservación Ecológica de los Centros de Población Cerro La Paila-Matías Rodríguez
Human settlement
First settlers According to the geoarchaeological evidence of the Cerro de las Navajas geosite, the territory of the Comarca Minera played a fundamental role in the economic development and military power of the pre-Columbian states of Mesoamerica, as it was the control center of exploitation and focal point of distribution of obsidian. These activities were carried out successively by the Teotihuacan (100 BC – 650 AD), Toltec (950–1100 AD) and Mexica (1325–1521 AD) cultures, extending until the early colonial period.
Geological explorations