Sierra Madre Occidental
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The Sierra Madre Occidental is a major
mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have aris ...
system of the North American Cordillera, that runs northwest–southeast through northwestern and western Mexico, and along the
Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...
. The Sierra Madre is part of the
American Cordillera The American Cordillera ( ) is a chain of mountain ranges (cordilleras), consisting of an almost continuous sequence of mountain ranges that form the western "backbone" of the Americas. Aconcagua is the highest peak of the chain. It is also the ...
, a chain of mountain ranges (cordillera) that consist of an almost continuous sequence that form the western "sounds" of
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
,
Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...
,
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
, and West Antarctica.


Etymology

The Spanish name ''sierra madre'' means "mother mountain range" in English, and ''occidental'' means "western", these thus being the "Western mother mountain range". To the east, from the Spanish ''oriental'' meaning "eastern" in English, the
Sierra Madre Oriental The Sierra Madre Oriental () is a mountain range in northeastern Mexico. The Sierra Madre Oriental is part of the American Cordillera, a chain of mountain ranges (cordillera) that consists of an almost continuous sequence of mountain ranges that ...
range or "Eastern mother mountain range" runs generally parallel to the Sierra Madre Occidental along eastern Mexico and the
Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...
. The range extends from northern
Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...
, a state near the Mexico–U.S. border at
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
, southeast towards to the
Trans-Mexican Volcanic Belt The Trans-Mexican Volcanic Belt (), also known as the Transvolcanic Belt and locally as the (''Snowy Mountain Range''), is an active volcanic belt that covers central-southern Mexico. Several of its highest peaks have snow all year long, and dur ...
and Sierra Madre del Sur ranges. The high
plateau In geology and physical geography, a plateau (; ; : plateaus or plateaux), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. ...
that is formed by the range is cut by deep river valleys. This plateau is formed from volcanic rock overlying a basement of metamorphic rock. This uplift has caused changes in weather patterns; increased rainfall occurring in the mountains has provided areas where ecosystems can form in wetter areas than surrounding land. This water source forms watersheds that provide the arid surroundings with water that makes it possible to irrigate and farm crops. The wet ecosystems are islands of biodiversity, differing significantly from what would otherwise be a desert landscape. Oak forests are the predominant plant life, and extend into the lowland deserts. This forest and canyon land provided a place for a variety of
indigenous people There is no generally accepted definition of Indigenous peoples, although in the 21st century the focus has been on self-identification, cultural difference from other groups in a state, a special relationship with their traditional territ ...
to live, until Spanish settlers with associated
mestizo ( , ; fem. , literally 'mixed person') is a term primarily used to denote people of mixed European and Indigenous ancestry in the former Spanish Empire. In certain regions such as Latin America, it may also refer to people who are culturall ...
s came into the area to found towns for the silver mines in the area. The major industries in the area now are
agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...
and forestry, which have become contentious because of
land degradation Land degradation is a process where land becomes less healthy and productive due to a combination of Human impact on the environment, human activities or natural conditions. The causes for land degradation are numerous and complex. Human activitie ...
and the native population's opposition to these practices.


Geography

The range trends from the north to southeast.
Canyon A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency t ...
s cut by the rivers of the wet western slopes exist in addition to those of the northeast slopes, notably the Copper Canyon.


Location

The range runs parallel to the Pacific coast of Mexico, from just south of the Arizona-Sonora border southeast through eastern
Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...
, western Chihuahua,
Sinaloa Sinaloa (), officially the (), is one of the 31 states which, along with Mexico City, compose the Federal Entities of Mexico. It is divided into 18 municipalities, and its capital city is Culiacán Rosales. It is located in northwest Mexic ...
,
Durango Durango, officially the Free and Sovereign State of Durango, is one of the 31 states which make up the Political divisions of Mexico, 32 Federal Entities of Mexico, situated in the northwest portion of the country. With a population of 1,832,650 ...
,
Zacatecas Zacatecas, officially the Free and Sovereign State of Zacatecas, is one of the Political divisions of Mexico, 31 states of Mexico. It is divided into Municipalities of Zacatecas, 58 municipalities and its capital city is Zacatecas City, Zacatec ...
,
Nayarit Nayarit, officially the Free and Sovereign State of Nayarit, is one of the 31 states that, along with Mexico City, comprise the Political divisions of Mexico, Federal Entities of Mexico. It is divided in Municipalities of Nayarit, 20 municipalit ...
,
Jalisco Jalisco, officially the Free and Sovereign State of Jalisco, is one of the 31 states which, along with Mexico City, comprise the 32 Political divisions of Mexico, Federal Entities of Mexico. It is located in western Mexico and is bordered by s ...
,
Aguascalientes Aguascalientes, officially the Free and Sovereign State of Aguascalientes, is one of the 32 states which comprise the Political divisions of Mexico, Federal Entities of Mexico. At 22°N and with an average altitude of above sea level it is pre ...
to
Guanajuato Guanajuato, officially the Free and Sovereign State of Guanajuato, is one of the 32 states that make up the Political divisions of Mexico, Federal Entities of Mexico. It is divided into Municipalities of Guanajuato, 46 municipalities and its cap ...
, where it joins with the Sierra Madre del Sur and the Eje Volcánico Transversal (Transverse Volcanic Axis) of central Mexico after crossing . The mountains range from from the
Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...
in the north, but begin to approach within of the
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...
in the south. These mountains are generally considered to be part of the much larger
American cordillera The American Cordillera ( ) is a chain of mountain ranges (cordilleras), consisting of an almost continuous sequence of mountain ranges that form the western "backbone" of the Americas. Aconcagua is the highest peak of the chain. It is also the ...
, the mountains extending from
Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...
down to these across western North America.


Regions

''Sierra Tarahumara'' or ''Tarahumara'' is the name for the region of the Sierra Madre beginning at the Durango border and extending north. This name comes from the Tarahumara natives. This is a dramatic landscape of steep mountains formed by a high plateau that has been cut through with canyons including Copper Canyon, larger and, in places, deeper than the
Grand Canyon The Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a mile (). The canyon and adjacent rim are contained within Grand Canyon Nati ...
. This plateau has an average elevation of with most of the more eroded canyons on the western slope, due to the higher moisture content. The highest elevations occur in the Tarahumara range. The exact elevations of the highest peaks are not known within accurate enough ranges to determine their relative elevation. The highest point is probably Cerro Mohinora, located at . Estimates for the height of the mountain start around and go up to . However, Cerro Barajas, at , may be as high as although other sources give as the elevation. Cerro Gordo, at , may have an elevation between and . The southern end of the mountains may be referred to as the Sierra Huichola. In this area, the Sierra Madre begins to give way to the
Basin and Range Province The Basin and Range Province is a vast United States physiographic region, physiographic region covering much of the inland Western United States and Northern Mexico, northwestern Mexico. It is defined by unique basin and range topography, charac ...
. Subranges of this area include the Sierra de Alica and the Sierra Pajaritos, both in Nayarit, and the Sierra los Huicholes, Sierra de Morones, Sierra Nochistlán, and
Sierra Fría The Sierra Fría is a mountain range in central Mexico. It forms the northwestern border of Aguascalientes state and extends into adjacent Zacatecas, west of the city of Aguascalientes City, Aguascalientes. Geography The Sierra Fría is the sout ...
extending eastwards into Jalisco, Zacatecas, and Aguascalientes.


Water

The mountains act as a source of water, in an otherwise
arid Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...
environment from the increased precipitation from the mountain range. As such, rivers that have headwaters in the mountains provide water for
irrigation Irrigation (also referred to as watering of plants) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has bee ...
in the surrounding lands. The need for water to irrigate prompted the construction of dams, which has been the source of several environmental concerns in the area. The northern end of the range is more arid; hence, the Yaqui River, which drains that area, is an important source of irrigation in the state of Sonora. The Yaqui drains into the
Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...
, as do the Fuerte River in Sinaloa and the Humaya River further south. The Río Grande de Santiago drains from the southern slopes of the Sierra Madre. Along the more arid eastern slopes of the mountains, the Nazas River and Aguanaval River drain the mountains into a closed basin. These mountains supply 90% of the water used for irrigation within the watershed. North of this system is the Conchos River which drains into the
Rio Grande The Rio Grande ( or ) in the United States or the Río Bravo (del Norte) in Mexico (), also known as Tó Ba'áadi in Navajo language, Navajo, is one of the principal rivers (along with the Colorado River) in the Southwestern United States a ...
. Along many rivers the arid conditions have caused courses to be dammed to provide water for irrigation. These dams have caused concerns along with those caused by other activities. The Yaqui has been dammed with three large reservoirs along its course. The Río Grande de Santiago has also been dammed, including the Aguamilpa Dam begun in 1991 and the El Cajón Dam upstream from it. To provide irrigation water for farming the dry basin, the Nazas river was dammed in the 1930s and 1940s. This has led to the former drainage lakes in the area drying up, and soil depletion from the elimination of the river as a source of soil. Due to the continued
logging Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidder, skidding, on-site processing, and loading of trees or trunk (botany), logs onto logging truck, truckserosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
on the slopes of hillsides has increased.


Human

Numerous small populations live in Copper Canyon, some of them around old missions. Many settlements consist of single families or small family groups near agricultural fields. There are also a few towns of note, including Creel, Chihuahua, with 5,000 inhabitants; it serves as a stop on the train line. South of Copper Canyon is the town of El Salto, Durango, situated along highway 40. To the west is Copala, Sinaloa. To the south live the indigenous Cora people in the towns of Jesús María and La Mesa del Nayar. In addition, 1,000 people live in the village of Huajimic in Nayarit. The Bolaños River valley of Jalisco is populated with mining communities, such as San Martín de Bolaños, which has a population of around 3,000. Few paved roads cross the mountains, meaning that travel times can be long, even between cities that are relatively close. In the north, Mexico Federal Highway 16 connects
Hermosillo Hermosillo (), formerly called Pitic (as in ''Santísima Trinidad del Pitic'' and ''Presidio del Pitic''), is a city in the center of the northwestern Mexican state of Sonora. It is the municipal seat of the Hermosillo municipality, the state's ...
, Sonora and La Junta, Chihuahua. In the mountains, the
La Entrada al Pacifico LA most frequently refers to Los Angeles, the second most populous city in the United States of America. La, LA, or L.A. may also refer to: Arts and entertainment Music * La (musical note), or A, the sixth note *"L.A.", a song by Elliott Smi ...
Corridor is an incomplete road intended to connect
Los Mochis Los Mochis () is a coastal city in northern Sinaloa, Mexico. It serves as the municipal seat of the municipality of Ahome. As of the 2010 census, the population was 362,613, which was 61 percent of the municipality's population. Los Mochis is th ...
, Sinaloa and Chihuahua.
Durango Durango, officially the Free and Sovereign State of Durango, is one of the 31 states which make up the Political divisions of Mexico, 32 Federal Entities of Mexico, situated in the northwest portion of the country. With a population of 1,832,650 ...
and
Mazatlán Mazatlán () is a city in the Mexican list of states of Mexico, state of Sinaloa. The city serves as the municipal seat for the surrounding , known as the Mazatlán Municipality. It is located on the Pacific Ocean, Pacific coast across from th ...
are connected by highway 40, around 24 degrees north latitude.


Geology

The Sierra Madre Occidental is a high plateau of volcanic rock that is eroded in areas to reveal a basement composed of plutonic and
sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...
rocks underlying the two groups of
extrusive Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contr ...
volcanics. The lower of these groups is a series of volcanic rocks formed by lava flows. The surface of the plateau is made up of a second series of volcanic
ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...
s, covered mostly by clay rich organic
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
s. Some
intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
s in the area have deposited ore veins that are commercially viable. The landscape was shaped after rock placement. Rivers cut valleys into the plateau, following folds in the rocks. Rocks have broken off of the slopes, forming rocky sides. The bedrock is covered by the clay rich soils, except in eroded areas, where water carries away deposits leaving a stony surface.


Geological history

The basement is thought to be Older North American basement, especially in the North, and a number of different accreted terranes, which are mostly covered by
Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...
volcanism. The northern extent of the Sierra Madre is the Cortés Terrane, although the northern extreme of this contains a small portion of the Carborca Terrane. Some of the northern end may also be underlain by a
Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...
basement placed around the same time as the
Grenville Orogeny The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, ...
. Some of this area has a series of
Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
sedimentary sequences from a deep marine environment underlying it, considered by some to be part of the Cotes Terrane and by others to be transported. In some areas, distinct sedimentary rocks can be identified by shallow-water
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
and Mississippian sedimentary rocks underlying deep-water Pennsylvanian and
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
, which are divided by Mississippian
rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...
. The Permian clastics contain some detrital rock that sit alongside low-grade metamorphosed sedimentary and volcanic rocks with serpentinite. South of the Cortes and Carborca Terranes is the San José de García Terrane, which is a combination of Cretaceous arc volcanics and volcaniclastics, which may be thrusting over the Cortes terrane. The southern part of the range is made up of the Guerrero Composite Terrane, a large body, which is actually a complex of five different subterranes, not all of them within the main body of the Sierra Madre. However, the terrane is mostly covered by volcanics and sedimentary deposits, so it is only visible where erosion has revealed it. The main subterranes of the Guerrero Composite Terrane that are within the Sierra Madre are the Tahue and Zihuatanejo terranes. Dividing the Guerrero Terrane from the rest of the Sierra Madre terranes is a boundary that is thought to represent the Early Cretaceous Arperos Basin, a marine basin which separated the island arc that came to form the Guerrero terrane from the accretions that came to form the Sierra Madre terrane. It contains a lower formation made up of
pillow basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% o ...
s with pillow breccias, tuffs, and
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
s underlying a group of
pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
s, oozes, and
turbidite A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...
s. Covering the southern basement are sedimentary and metamorphosed sedimentary rocks containing
argillite Argillite () is a fine-grained sedimentary rock composed predominantly of Friability, indurated clay particles. Argillaceous rocks are basically lithified muds and Pelagic sediment, oozes. They contain variable amounts of silt-sized particles. T ...
, limestone, volcanic schist,
slate Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic ro ...
, and
greywacke Greywacke or graywacke ( ) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and Sorting (sediment), poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size Lith ...
which were exposed in the canyon of the Santiago River. Near these sediments late
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
to early
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
and
granodiorite Granodiorite ( ) is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...
intrusive bodies occur. A possible cause of this is that these bodies were roof pendants which were uplifted by plutons. Mesozoic limestone also occurs in northern portion of the mountains, mostly from the Cretaceous. Towards the end of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
, the
Laramide orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the o ...
increased the activity of magmatism in the area, forming the first major igneous series in the area. The igneous series are made up of formations of plutonic and volcanic rock, which would later be exposed. Interbedded with these rocks are sedimentary deposit rocks. In the center of the range, some of these rocks have been deformed by tectonic forcing that occurred at the same time. The southern part of the range contains none of the volcanism that is apparent in the northern range. These formations ended in the
Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
.
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
volcanism formed a series of andesitic and rhyolitic formations in the area, with spatial and temporal variations throughout. Most of the
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
and
silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
deposits are also in these rocks. In the Oligocene, ash flows became the predominant deposit of the area, with interbedded lava flows between. These ash flows began the second series of high magmatism formations. The Mid-Tertiary ignimbrite flare-up formed a series of ignimbrite formations, layered one atop another, that are sometimes broken by lava flows. The ignimbrite formations in this area cover the largest area of any known series, with ten
caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...
s identified in the province. Three of these calderas are in Copper Canyon. The lava has formed a series of
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
rocks that comprise the Southern Cordilleran Basaltic Andesite Suite. The tuffs are above a thick formation of lava rock. Around five or six units have been identified, mostly around the Copper Canyon area. These tuffs have allowed wide-ranging correlation with formations in other geographical areas, for example
Death Valley Death Valley is a desert valley in Eastern California, in the northern Mojave Desert, bordering the Great Basin Desert. It is thought to be the Highest temperature recorded on Earth, hottest place on Earth during summer. Death Valley's Badwat ...
. During the Miocene, three periods of volcanism marked separate events in the Sierras. Each period is marked by different volcanic processes. The first was a continuation of the Oligocene flare-up, which lasted through the early Miocene. This may be a distinct second occurrence of the same process, placing silica-rich lava above Oligocene rocks. Also in the early Miocene more intermediate basaltic andesites occur along faults and in grabens. Beginning in the early Miocene and continuing into the middle, an arc of andesite was placed during the spreading of the
Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...
. The basin and range-style faulting of the middle-late Miocene took place at the same time as the placement of alkali basalts, In the westernmost slopes mafic dikes formed. These events have also been linked to the subduction of the Farallon Plate. Episodes of volcanism continued into the
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...
.


Structures

The Sierras are believed to be a thick core covered by volcanics and eroded by numerous rivers. Some have suggested that the basement of the mountains have numerous intrusions made by mafic
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
. At their surface, the mountains are made up of large-scale ignimbrite sheet that has been incised by rivers flowing from rainfall in the mountains. The surface of the plateau is almost exclusively from the second series of flows causing the rock that is most visible to be ignimbrites with lava flow layers. The region has a general strike from just west of north to just south of east. Faults in the area tend to be younger than the upper volcanics, excluding those associated with calderas, but do occur in distinct periods. The large faults along the eastern slope have caused the slope to be made up of large
escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. Due to the similarity, the term '' scarp'' may mistakenly be incorrectly used inte ...
s that face into the interior basins. These faults are commonly covered by
alluvium Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...
and
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
, making them difficult to discern, but can be found in certain
fault block Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by Tectonics, tectonic and localized stresses in Crust (geology), Earth's crust. Large areas of bedrock are broken up into blocks by Fault (geology) ...
s.
Graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
s have formed in the north, and some of these are filled with volcanic and sedimentary floors, and long depressions have formed in the southern Sierra Madre. The faulting decreases in the center of the range where the faults are mostly small normal faults, but increases once again on the western slope. In fact, the major normal faults tend to diverge around the center of the core and join at either end. Some of these faults may have allowed ignimbrites to erupt from the surface, and so there may be some association between the ignimbrite occurrence and faults; this can be used to find out
information Information is an Abstraction, abstract concept that refers to something which has the power Communication, to inform. At the most fundamental level, it pertains to the Interpretation (philosophy), interpretation (perhaps Interpretation (log ...
about different kinds of basement rock present. There are two faults dividing the Sierra Madre from the central
Mexican Plateau The Central Mexican Plateau, also known as the Mexican Altiplano (), is a large arid-to-semiarid plateau that occupies much of northern and central Mexico. Averaging above sea level, it extends from the United States border in the north to the T ...
. The more southern one is the north–south Aguascalientes fault extending from Altos de Jalisco to near Zacatecas, where it joins the more northern northwest–southeast trending San Luis–Tepehuanes fault extending from Guanajuato to Durango. The southern boundary of the Sierra Madre Occidental with the Jalisco block is a series of folds,
thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...
, and left
lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...
faults date from the middle Miocene. This may be evidence for a left transpressional shear zone. The area between this boundary and the Aguascalientes fault is filled with numerous grabens and half-grabens, as well an east–west left shear zone, the El Roble shear zone. At the west end of these grabens and half-grabens are the Pochotitan and the more northerly San Pedro fault systems, which form the western boundary of the faults in the southern mountains. In the north there is an unknown boundary between the Cortes Terrane and the Guerrero Composite Terrane. Some theorize that this is a section of the Mojave–Sonora Megashear, but this theory is not universally accepted; however, the Megashear is important, and, in fact, is necessary for reconstructions of the opening of the Gulf of California, as of 2003.


Mineral deposits

On a smaller scale, mineral deposits are distributed in formations of the Sierra Madre, although the events that placed these deposits vary throughout the mountains. The Guerrero composite terrane contains many of the economic deposits, often found in ore bodies younger than the Cretaceous. Gold and silver deposits most commonly occur in the altered andesites of the early volcanics, typically these deposits are between 30 and 50 million years old. These are believed to be caused by later
intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
s into the early flows. Fissure-vein deposits have been divided into two groups of fissure
vein Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and feta ...
deposits, which are divided geographically into an eastern and western series. In the east, the gold and silver are accompanied by
lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
and
zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
. In the south, the Bolaños mine district is contained with the Bolaños Graben. Some also occur as epithermal deposits. Also, some gold occurs along with
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
in Cenozoic iron-oxide skarn and replacement deposits along the Pacific. In addition to gold and silver and their related deposits, tin,
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
, and mercury occur, sometimes in later units, mostly in later volcanics, and
Molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
occurs in the mountains, often along with older copper deposits or in Oligocene deposits in the east. The belt of tin deposits lies mostly within the eastern slopes from Durango to Guanajuato. In these areas, tin occurs in rhyolitic ignimbrites in many, possibly over 1000, small deposits of
cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...
. Typically these deposits are divided from overlying ignimbrites by breccia, which may also contain ore. Many of these are thought to be hydrothermal deposits To the east of these units is a belt of more mercury deposits, followed by another belt of
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
deposits, although these deposits are mostly limited to Chihuahua and Hidalgo. Iron occurs in three different regions placed by different mechanisms. Along the Pacific there the numerous skarn and replacement deposits mentioned above with relation to gold. Iron occurs in Durango in the form of
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
lava flows, which are often surrounded by smaller
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
deposits, thought to be ash flows. There is also a belt of iron deposits further east.


Soil

Most soil in the mountains is covered by an organic-rich layer over layers rich in
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
. Soils are commonly phaeozems that are up to . Some soils are cambisols that are less than deep and well- drained. Due to the high clay content, which blocks water from being absorbed into the soil, larger rock particles in the soil help reduce runoff and soil losses from erosion. Areas that are covered in stone are known as lithosols, and make up most of the remaining surface in the mountains, especially on upper slopes. The last major soil type are vertisols, which are thin mineral-poor soils. Soils at higher elevations experience more leaching, due to increased rainfall.
Acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
ic soils may have lower
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
content, leading to lower plant soil quality. Soils along the eastern slopes have increased organic content and a clay heavy layer that is developed more than those of the more arid eastern lands. The thickness of soil layers also increases. Problems with
soil degradation Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a soil health, stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession revert ...
have been aggravated by the cultivation of drug crops, leading to
deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...
of many areas. Other problems include
overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature ...
, which has led to terracing from cattle paths and the formation of a soil crust, and soil acidification, which poses a risk to some grasslands as of 2002.


Climate

The climate varies considerably between the northern and southern extents of this long mountain range. Seasonal variations also occur due to the presence of large bodies of warm water delivering warm damp air from each side of the range. This region undergoes a seasonal variety with two wet seasons, including a summer
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
, and two dry seasons each year.


Temperature, pressure, and wind

Air pressure changes in northwestern Mexico and the southwest United States are the main causes of seasonal variation in the Sierra Madre. A high pressure area that rests over the mountains in the winter begins to move north of the mountains into
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
during the month of June. The high pressure begins to break down and move south during September or October; however, the breakdown is usually at a slower pace than the movement north. This high pressure belt is associated with the mechanics that form the Bermuda High. The climate in the mountains is mild. Summer temperatures maintain a constant level. Maximum temperatures are typically in July at around 31 C with average temperatures of the order of 16 C during this same period. Mean annual temperatures are between above . Below-freezing temperatures can occur in the higher mountains, with
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
occurring as snowfall certain times of year. During the summer monsoon,
wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...
patterns undergo large-scale changes. In May there is very little large-scale wind current through the mountains, most circulates around the mountains, although onshore flow is present. As the high pressure moves north, air is pulled off the Gulf of Mexico, bringing easterly winds aloft to the mountains. On the east slope of the mountain, daytime upslope winds flow to the crest, where the flow joins westerly winds. The mountains cause convection during the following monsoon season, during which nocturnal winds at low levels in the atmosphere move moisture overnight. Extensive lightning activity occurs during this season. After the high pressure breaks down, wind patterns return to those prior to the monsoon season.


Precipitation and humidity

Precipitation varies on both annual and seasonal scales in the Sierra Madre. Annual differences in regional climate are associated with the El Niño-Southern Oscillation with El Niño years leading to a wetter climate. Monsoon rains come to the Sierra Madre in June as the high pressure area moves north, leading to wet summer seasons. This causes east winds bringing
moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...
from the
Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...
. On the western side of the mountains, which are affected by the largest change in precipitation between the
dry season The dry season is a yearly period of low rainfall, especially in the tropics. The weather in the tropics is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back over the course of the year. The t ...
and monsoon season, in the monsoon season rainfall can exceed in a single month. The southern region receives more of the rainfall than the northern. Much of this precipitation occurs as tropical storms. As the high pressure over New Mexico breaks down, rainfall in the Sierra Madre ends. Because of the monsoon, the summer accounts for the majority of rainfall in the area. The spring and fall dry season separate out a weaker wet season in the winter. In addition to increasing in the southern ranges of the mountains, rainfall increases in the higher elevations of the Sierra Madre Occidental.
Humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
in the mountains varies at wide levels as does rainfall. In the early morning before dawn, the air is almost saturated (often over 90%
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
) near the mountain tops with low clouds over the range. Lower in the range, air is not as near saturated in the morning. Seasonal variation in humidity is also present with average May and June relative humidity around 50%, with 25% possible during the day. Also during the day, relative humidity drops and cloud levels rise as temperatures rise. The humidity of the range is also influenced by the same seasonal changes as rainfall. In the dry season
dew point The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to produce a relative humidity of 100%. This temperature depends on the pressure and water content of the air. When the air at a temperature above the ...
s are low at high elevations (500 hPa), around in the south of the range, and in the north in May. In June, dew points begin to increase from the May levels up to in the north and in the south. By July these dew points are at throughout the range. The range allows higher dew points throughout these periods than the surrounding low lands. This rise in humidity accompanies the monsoon.


Ecology

The mountains create a diverse setting for plants and animals by creating a different set of conditions from the surroundings. The Sierra Madre Occidental pine-oak forests are found at elevations of throughout the range, but the forests in the mountains vary by elevation and place in the range. This ecoregion is noted for its high
biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...
and large number of
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
species, and for allowing some species to extend their range.


Flora

The dominant plants vary across the range, and the habitat that they present varies from scattered
woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...
to both
deciduous In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...
and
coniferous Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
forest. The elevation and latitude in the range are the major determining factors in the dominant plants. Oaks dominate the lower reaches of the mountains, where stands grow down to about . Some oak species even continue into the surrounding ecosystems. In the western slopes of the range,
cloud forest A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest, is a generally tropical or subtropical, evergreen, Montane forest, montane, Tropical and subtropical moist broadleaf forests, moist forest characteri ...
also occurs, mostly on mid-elevation slopes with little exposure to wind or sun in the southern end of the range. At higher elevations
pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...
s begin to grow alongside the oaks, and pines begin to dominate the oaks at higher elevations. At high elevations and in the north, mixed conifer forests become the dominant ecosystem. These forests are composed primarily of pines and
fir Firs are evergreen coniferous trees belonging to the genus ''Abies'' () in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genu ...
s, which begin to grow at these elevations. There are also
grasslands A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes such as clover, and other herbs. Grasslands occur ...
on some mountain tops, surrounded by the forest that occur in those areas. Plants in the area typically have large responses to the change in climate with each season. Monsoon season is the largest of these effects, with leaf buds following only a few months after the rains begin. Flowering season occurs in the months preceding the summer monsoon. This is only the peak flowering season, with plants flowering throughout the year. Due to the early flowering,
fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...
is ripe and
seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...
s are dispersed at the beginning of the rains. There are also areas where plants have little response to the seasons, particularly those areas that experience moist conditions, caused by the elevations. These plants may maintain leaves through times when other areas are in the dry season, during which most deciduous trees have no leaves.


Fauna

The mountains are often a corridor for species allowing more diversity in the area, by combining species from different regions. Animals typically associated with arid and mountainous habitats share the mountains with species associated with habitats further south. There are many carnivorous and omnivorous mammals native to the area, although several are extirpated or are part of threatened populations. The Mexican wolf's range in the mountains is limited to the foothills of Durango or the animal may have been extirpated; the black bear population is small, and the Mexican grizzly bear that once resided here is confirmed extinct.
Jaguar The jaguar (''Panthera onca'') is a large felidae, cat species and the only extant taxon, living member of the genus ''Panthera'' that is native to the Americas. With a body length of up to and a weight of up to , it is the biggest cat spe ...
s and
ocelot The ocelot (''Leopardus pardalis'') is a medium-sized spotted Felidae, wild cat that reaches at the shoulders and weighs between on average. It is native to the southwestern United States, Mexico, Central America, Central and South America, ...
s are also now rare. On the other hand,
mountain lion The cougar (''Puma concolor'') (, ''Help:Pronunciation respelling key, KOO-gər''), also called puma, mountain lion, catamount and panther is a large small cat native to the Americas. It inhabits North America, North, Central America, Cent ...
and
bobcat The bobcat (''Lynx rufus''), also known as the wildcat, bay lynx, or red lynx, is one of the four extant species within the medium-sized wild cat genus '' Lynx''. Native to North America, it ranges from southern Canada through most of the c ...
are more common. On the eastern slopes there are American badger,
coyote The coyote (''Canis latrans''), also known as the American jackal, prairie wolf, or brush wolf, is a species of canis, canine native to North America. It is smaller than its close relative, the Wolf, gray wolf, and slightly smaller than the c ...
and
gray fox The gray fox (''Urocyon cinereoargenteus''), or grey fox, is an omnivorous mammal of the family Canidae, widespread throughout North America and Central America. This species and its only congener (biology), congener, the diminutive island fox ...
that live across the mountains. Native ungulates include the white tailed deer,
mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whit ...
, and
collared peccary The collared peccary (''Dicotyles tajacu'') is a peccary, a species of artiodactyl (even-toed) mammal in the family Peccary, Tayassuidae found in North America, North, Central America, Central, and South America. It is the only member of the gen ...
. Rodents and lagomorphs include the
eastern cottontail The eastern cottontail (''Sylvilagus floridanus'') is a New World cottontail rabbit, a member of the family Leporidae. It is the most common rabbit species in North America. Distribution The eastern cottontail can be found in meadows and shrub ...
, which lives in the forests of the western slopes, cliff chipmunk, rock squirrel, Mexican fox squirrel, and various species of
Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At over 870 species, it is either the largest or second-largest family ...
.
Raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the North American, northern or common raccoon (also spelled racoon) to distinguish it from Procyonina, other species of raccoon, is a mammal native to North America. It is the largest ...
s, hog-nosed skunk, and hooded skunk live in the mountains. The white-nosed coati lives on the western slopes, and the ring-tailed cat lives throughout. Many species of bats live in the mountains also. A variety of
lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
s live in the area and surroundings. The Tarahumara frog lives in the oak and pine stands preferring moving water to pools. The southern extent of the Sonoran mountain kingsnake's range is the Chihuahuan desert into the mountains. Other snakes and frogs live in the mountains, and many species live in the western slopes. Birds frequent the mountains, some as a migratory path and others as
native species In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often popularised as "with no human intervention") during history. The term is equi ...
. The migratory birds often use the area to the west as an overwintering area, and migrate north along the western slopes. In the northern canyons birds may be divided into different
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
s, or more specifically, the different types of forest, leading to differences in range by elevation. Some of this difference by elevation may even extend the range of some species, enabling tropical species to use the mountain valleys for migration. Bird species
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
to the Sierra Madre Occidental include tufted jay, the "gray-eared" subspecies of red warbler, eared quetzal, thick-billed parrot, and formerly included the imperial woodpecker, which now may be extinct. The rivers and streams of the range contain some of the southernmost
trout Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...
populations in North America. These populations may be native, although this is not universally accepted. Invasive fish compete with the native species which has been a cause of concern among researchers, along with concerns about the effects of logging on these species.


Surroundings

The
Sonoran Desert The Sonoran Desert () is a hot desert and ecoregion in North America that covers the northwestern Mexican states of Sonora, Baja California, and Baja California Sur, as well as part of the Southwestern United States (in Arizona and California). It ...
is found in the northwestern foothills at . The Chihuahuan Desert is found to the northeast and east, the Meseta Central matorral and Central Mexican matorral to the southeast, and the Sinaloan dry forests to the west and southwest. These lower elevations are usually graded into by a stand of tropical deciduous forest, which has a large portion of flora made up of
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s and
legume Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...
s. These flowering plants are mostly from the genus '' Bursera''. The ecotone, made up of the tropical deciduous forest, is commonly sparsely populated, sometimes only by small stands of trees. It may be referred to as
savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...
.


Preservation

Preservation efforts in the modern day include those of Edwin Bustillos. Other groups, including
Conservation International Conservation International (CI) is an American nonprofit environmental organization headquartered in Crystal City, Virginia, in Arlington County, Virginia. CI's work focuses on science, policy and partnership with businesses, governments and co ...
, work to protect animal species in the area. Basaseachic Falls National Park is a
national park A national park is a nature park designated for conservation (ethic), conservation purposes because of unparalleled national natural, historic, or cultural significance. It is an area of natural, semi-natural, or developed land that is protecte ...
in the mountains containing the highest
waterfall A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in seve ...
s in the country. Cumbres de Majalca National Park was designated in 1939. Additionally, there are reserves such as La Michilía in the southern Sierra Madre, or the Tutuaca reserve in western Chihuahua, which was established in 2000 under a new system of management. Other protected areas in the Sierra include the Bavispe, Campo Verde, Cerro Mohinora, Papigochic, and Sierra de Álamos–Río Cuchujaqui flora and fauna protection areas. The
Cuenca Alimentadora del Distrito Nacional de Riego 043 Estado de Nayarit The Cuenca Alimentadora del Distrito Nacional de Riego 043 Estado de Nayarit is a protected natural areas of Mexico, protected natural area in west-central Mexico. It extends across portions of southern Sierra Madre Occidental and the westernmost ...
, established in 1949 to protect forests and watersheds, is now a natural resources protection area which conserves much of the southern Sierra.


People and history

The mountains are home to several indigenous nations speaking
Uto-Aztecan languages The Uto-Aztecan languages are a family of native American languages, consisting of over thirty languages. Uto-Aztecan languages are found almost entirely in the Western United States and Mexico. The name of the language family reflects the common ...
, including the Tarahumara in the central portion of the range, the Huichol in the southern part of the range, and the Tepehuanes in the eastern slopes.


Prehistory

Archaic cultures are known to have inhabited the Sierra Madre along with the rest of the surrounding lands, but little is known of the culture, although it does vary between the northern and southern extremes of the range. The agrarian Chalchihuites Culture began as farming communities around the first century AD and remained small communities until 300 AD when new agricultural techniques caused a large growth in population until around 500 AD. This culture began to decline in the ninth century. The Mogollon culture has been described in the northern foothills. Sites date the emergence of the culture to around 900 AD, and its abandonment to around 1000–1100 AD. During the period estimated for Mogollon abandonment, the Rio Sonora culture began agricultural developments along the Rio Sonora and rivers flowing into it. This culture produced
pottery Pottery is the process and the products of forming vessels and other objects with clay and other raw materials, which are fired at high temperatures to give them a hard and durable form. The place where such wares are made by a ''potter'' is al ...
and lived in pit houses, until 1150 to 1200 when they began to construct surface dwellings. Construction of these houses ended around AD1550.


Spanish Sierra Madre

Francisco de Ibarra came to
Durango Durango, officially the Free and Sovereign State of Durango, is one of the 31 states which make up the Political divisions of Mexico, 32 Federal Entities of Mexico, situated in the northwest portion of the country. With a population of 1,832,650 ...
in 1554, and began to settle the area. He would explore the western coast and cross the Sierra Madre in 1564. Early Spanish influence in the area came from the new silver mines, the first of which was established in 1567 at Santa Barbara. As sites opened for mining,
missionaries A missionary is a member of a religious group who is sent into an area in order to promote its faith or provide services to people, such as education, literacy, social justice, health care, and economic development.Thomas Hale 'On Being a Miss ...
came to the areas and had a strong presence by 1595. The first meeting with the Tarahumara came in 1607, when a missionary went up the valley to meet them. Opposition to the missionaries built up, leading to the Tepehuán Revolt. This revolt began in 1616 in the town of Santa Catarina de Tepehuanes in Durango, and lasted for two years. The discovery of silver at Parral in 1631 led to the northern limit of settlement moving into Tarahumara lands. The
Jesuits The Society of Jesus (; abbreviation: S.J. or SJ), also known as the Jesuit Order or the Jesuits ( ; ), is a religious order (Catholic), religious order of clerics regular of pontifical right for men in the Catholic Church headquartered in Rom ...
renewed missionary activity in the 1630s, with a new program that increased in scope until around 1650. Tarahumara moved further into the mountains in order to escape the conditions. A smallpox epidemic caused a revolt in 1645. A revolt arose in 1648, primarily among the Tarahumara. A
drought A drought is a period of drier-than-normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, ...
caused a pair of revolutions in 1650 and 1652. The last major revolt began in March 1690 among the Tarahumara and ended in 1698. Demands from labor drafts increased in the 1720s, placing a new pressure on missions. Criticism of the Jesuits rose in the 1730s with complaints of Jesuit Commerce, which was established by mission stores. In 1767, Jesuits were expelled from New Spain, ending the mission program. A new colonial official,
José de Gálvez José is a predominantly Spanish and Portuguese form of the given name Joseph. While spelled alike, this name is pronounced very differently in each of the two languages: Spanish ; Portuguese (or ). In French, the name ''José'', pronounced ...
, came to New Spain and established new laws that caused a boom in silver mining activity in the 1770s. After the
Apache The Apache ( ) are several Southern Athabaskan language-speaking peoples of the Southwestern United States, Southwest, the Southern Plains and Northern Mexico. They are linguistically related to the Navajo. They migrated from the Athabascan ho ...
faced heightened resistance to raiding from the Spanish in Chihuahuan, they moved down to the Sierra Madre in 1794. By 1800, raiding had essentially ended.


Mexican Sierra Madre

After leaving San Carlos in the fall of 1881, Geronimo and other Apache moved to the mountains, and became known as the ''Nednai'', sometimes referred to as the "Pinery Apache" or "Bronco Apache". From there they raided Sonora and the surrounding land until General
George Crook George R. Crook (September 8, 1828 – March 21, 1890) was a career United States Army officer who served in the American Civil War and the Indian Wars. He is best known for commanding U.S. forces in the Geronimo Campaign, 1886 campaign that ...
entered the mountains in 1883 to discuss Geronimo's return. Geronimo eventually surrendered in 1886.
Pancho Villa Francisco "Pancho" Villa ( , , ; born José Doroteo Arango Arámbula; 5 June 1878 – 20 July 1923) was a Mexican revolutionary and prominent figure in the Mexican Revolution. He was a key figure in the revolutionary movement that forced ...
fled to the mountains in 1894, becoming a bandit.


19th century

Railroads came to the area starting in the 1880s and 1890s, which allowed many old mines in the region to reopen at a profit. Since most of the railroads were American, the foreign influence led to unrest among the people living in the mountains, causing the Tomochic rebellion in 1892. In addition to the railroads, canals were constructed in the 1890s in the Yaqui and Mayo river valleys. These canal projects failed, however, owing to the resistance that the natives of the valleys put up against the projects. Loggers began arriving in the mountains in the late 1800s. In response to the new industry, the Tarahumara moved further into the canyons.


20th century

The 1910 revolution began in Chihuahua and spread over the mountains throughout the winter of 1910–1911. Silver mines were forced to make payments to the rebels, but were allowed to continue operating. General John J. Pershing began to follow Pancho Villa in 1916 and entered the mountains; however, he received no information from the local population. The raids subsided by 1919, and Villa returned peacefully to the foothills. In order to construct irrigation projects in the lowlands below the valleys, irrigation projects were never completed in the Sonoran hills; instead, the Yaqui River was dammed in the 1930s. Dams continued to be constructed in the 1940s and 1950s on the Yaqui River and its tributaries with the largest reservoir, behind the Álvaro Obregón Dam completed in 1952. Dams were also constructed on the Mayo river. Because of the dams, soil condition deteriorated, and more work was required to improve soil quality. The mountain range was crossed by the Ferrocarril Chihuahua al Pacifico
railroad Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
, completed in 1961. The railroad went up for sale in 1996, but no transaction was ever completed.


See also

* List of birds of the Sierra Madre Occidental * Sierra Madre * Sierra Madre Occidental pine-oak forests *
Sierra Madre Oriental The Sierra Madre Oriental () is a mountain range in northeastern Mexico. The Sierra Madre Oriental is part of the American Cordillera, a chain of mountain ranges (cordillera) that consists of an almost continuous sequence of mountain ranges that ...


References


External links

* {{Authority control Landforms of Aguascalientes Landforms of Chihuahua (state) Landforms of Durango Landforms of Guanajuato Landforms of Jalisco Landforms of Nayarit Landforms of Sinaloa Landforms of Zacatecas Madre Occidental Mountain ranges of Sonora Mountain ranges of the Sonoran Desert North American Cordillera Pacific Coast of Mexico Physiographic provinces Physiographic regions of Mexico Volcanism of Mexico