Caballo Mountains
Encyclopedia
The Caballo Mountains, are a mountain range located in Sierra
and Doña Ana Counties
, New Mexico
, United States
. The range is located east of the Rio Grande
and Caballo Lake
, and west of the Jornada del Muerto
; the south of the range extends into northwest Doña Ana County. The nearest towns are Truth or Consequences
and Hatch
.
Most of the Caballo Mountains are located on land owned by the Bureau of Land Management
. The mountains are unusual, and perhaps unique in New Mexico, for the relatively complete geologic history revealed by their rocks. Vehicular access to the range is by Interstate 25
from the west, by New Mexico State Road 51 from the north, and by several dirt roads from the east.
of approximately 3,400 feet.
The types, sizes, and profiles of the Caballo watersheds vary significantly according to the part of the range that they drain. No perennial streams flow through the mountains, although the course of the Rio Grande is close to the north, west, and south margins of the range. The northern part of the Caballos drains into the Rio Grande through Ash Canyon and Mescal Canyon. The confluences of those two intermittent streams are just below Elephant Butte Dam
. Water falling on the precipitous west face of the range drains directly into the Rio Grande by means of numerous first order canyons with high gradients. All are ephemeral
and less than 3 miles in length.
In contrast, the eastern side has only two primary drainages, each with a much lower gradient than those to the north and west. Water falling on the southern half of the east side flows into Barbee Draw. After joining another tributary near Point of Rocks to form Rincon Arroyo, this ephemeral drainage flows southward before joining the Rio Grande near Rincon, New Mexico
. The length of this drainage is over 25 miles. The north portion of the east side is drained by Jornada Draw. This drainage, however, is endorheic
and has no surface connection to the Rio Grande.
compares the formation's bedding location in comparison with other formations nearby. This allows not only the identification of the older and younger formations, but conclusions about unusual local conditions, such as folding
, a fault displacement, or an unconformity
. Absolute dating
measures the presence and ratios of chemicals within the rocks to determine the number of years since they were deposited. The conditions existing when the rock was deposited can be determined by examining its type (igneous, metamorphic, or sedimentary), the orientation and size of crystals or sediments within it, and the orientation of the formation within its larger regional setting. By studying plant and animal fossils that may exist in the formation, it may be possible to determine not only its relative age, but the climate
at the time of deposition.
Weathering
and erosion
remove any rock that is exposed at the surface of the Earth. Consequently, there are no sites where all rocks deposited at that location have been preserved. Certain sites, however, may have more complete geological histories because of differences in the timing and circumstances of rock removal. The Caballo Mountains are essentially unique in New Mexico because their section of exposed rocks begins in Precambrian
time, and runs through every geological period of the Phanerozoic
eon with the exceptions of the Triassic
and Jurassic
. This provides an unparalleled picture of the geological history of southern New Mexico.
, and metamorphic amphibolite
and gneiss
. These rocks date from the Early to Middle Proterozoic
, and are found along the base of the larger fault blocks.
Throughout the early and middle Paleozoic
southern New Mexico alternated between being flooded by shallow tropical seas, and being exposed to erosion. Sedimentary deposits of early and middle Paleozoic age include:
An unconformity
exists above the Lake Valley Formation, and appears to include the middle Mississippian through the early Pennsylvanian
periods. During the Pennsylvanian and Permian
periods, a major deformation created a series of uplifts and intermontane basins. This event is often referred to as the Ancestral Rocky Mountains. Associated with this event is the Magdalena Group, which includes deposits of both marine and non-marine sources. The thickness of these strata is greater than that of all earlier Paleozoic rocks. Above the Magdalena Group is the Red House Formation of packstone and shale, the Nakaye Formation of limestone, the Bar B Formation of interbedded limestone, dolomite, shale, and conglomerate
, and the red shale beds of the Abo Formation. All of those strata are Pennsylvanian in age. Above them is thePermian Yeso Formation, which consists of sandstones, siltstone-dolomites, and limestones. The Paleozoic strata are completed by the Meseta Blanca Sandstone.
Most of the Mesozoic
rocks are missing from the Caballo geological history. A second unconformity lies above the Meseta Blanca Sandstone, and includes all of the Triassic
and Jurassic
periods. The next oldest rocks are of Cretaceous
age and include:
The Mesozoic rocks terminate below another unconformity. Above that is the Love Ranch Formation of conglomerate, mudstone and sandstone, which was deposited in the Paleocene
to early Eocene
. During the Eocene
, a wave of arc volcanism was felt across southern New Mexico. In the Caballo Mountains, this can be seen in the Palm Park Formation, a thick layer of andesitic or tuffaceous mudstones, sandstones, and breccia
. Next is the Bell Top Formation, which consists of rhyolite
, basalt flows, and tuffaceous sandstones. In the southern part of the Caballo Mountains, there are remnants of a region wide sheet of flood basalts and andesite, which was laid during the Oligocene
. Of similar age is the Thurman Formation of white sandstone. The Santa Fe Group was deposited during the Miocene
and Pliocene
.This thick layer consists of the Hayner Ranch Formation (conglomerate, sandstone and shale), the Rincon Valley Formation (conglomerate, sandstone, and mudstone), the Selden basalts, and the Camp Rice/Palomas Formations (ash fall deposits, basalts, and pumice
-clast conglomerates). Quaternary
and Holocene
deposits consist of alluvium
. On the west side of the range along the Rio Grande, the alluvial fill consists of unconsolidated fluvial
deposits of boulders, cobble
, and gravel. In the closed basin on the east side of the range, there are relatively few fluvial deposits. Instead, the sediment includes a flat, thin veneer of sand and gravel.
in the north to the state of Chihuahua, Mexico
in the south. It is the product of extensional
tectonic (or divergent) forces that formed a series of basins between the Colorado Plateau
and the North American craton
Thin continental crust
, normal fault block topography, high regional elevation, and volcanism
is found over the course of the rift.
The history of movement along the rift has been divided into three separate stages: an initial stage during the late Eocene to early Oligocene
, a second stage during the late Oligocene to late Miocene
, and a third stage beginning in the late Miocene or early Pliocene
and continuing to the recent past. Activity in the vicinity of the Caballos during the first stage included explosive rhyolitic eruptions from cauldrons located to the northwest, west, and southeast. The earliest eruptions took place in the Dona Ana Mountains
and Organ Mountains
between 36.2 and 35.4 Ma. The Emory cauldron, located in the Black Range
, was active approximately 34.9 Ma. What is now the San Mateo Mountains (Socorro County)
contained at least two cauldrons, the Nogal Canyon cauldron (28.6 Ma) and the Mount Withington cauldron (27.4 Ma). Local subsiding appears to have begun around 34.9 Ma. The Caballo Mountains began to rise in the late Oligocene, and throughout the Miocene. Approximately 9.6 Ma, the eruption of basalts near Fort Selden
signaled the renewal of crustal extension and volcanism in the southern part of the rift. Activity along both older and new faults increased the number, but decreased the width of basins along this portion of the rift.
It has been estimated that the total value of copper, silver, gold, and lead produced from the Caballos before 1952 did not exceed $200,000. At present, more fluorspar is produced than any other mineral. The largest fluorspar deposits are found in Precambrian granite, and jasperized Fusselman Dolomite.
Soils on the mountains are generally rocky and thin.
Plant communities can be generally characterized as Chihuahuan desert scrublands, creosotebush desert, and desert grasslands. Dominant shrub species include creosote bush
(Larrea tridentata), honey mesquite
(Prosopis glandulosa), soaptree yucca
(Yucca elata), and four winged saltbush (Atriplex canescens
). Common grasses include black grama
(Bouteloua eriopoda), blue grama
(Bouteloua gracilis), sideoats grama
(Bouteloua curtipendula), and alkali sacaton (Sporobolus airoides
).
The most common mammalian predators are mountain lions (Felis concolor) and coyotes (Canis latrans). Other common mammals are Black-tailed jackrabbit
(Lepus californicus), desert cottontail
, (Sylvilagus auduboni) and kangaroo rats (Dipodomys merriami and Dipodomys spectabilis).
Common birds of prey include golden eagles (Aquila chrysaetos), Swainson's hawk
(Buteo swainsoni), Northern harrier (Circus cyaneus), and burrowing owl
(Athene cunicularia). Other birds include roadrunner
(Geococcyx californianus), quail
(Callipepla gambelii and Callipepla squamata), doves
(Zenaida macroura and Zenaida asiatica).
Common reptiles include Collared lizards
(Crotaphytus collaris), Roundtail Horned Lizard
(Phrynosoma modestum), Striped whipsnake
(Masticophis taeniatus), and Western diamondback rattlesnake (Crotalus atrox
).
Sierra County, New Mexico
-2010:Whereas according to the 2010 U.S. Census Bureau:*85.6% White*0.4% Black*1.7% Native American*0.4% Asian*0.0% Native Hawaiian or Pacific Islander*3.3% Two or more races*8.6% Other races*28.0% Hispanic or Latino -2000:...
and Doña Ana Counties
Doña Ana County, New Mexico
-2010:Whereas according to the 2010 U.S. Census Bureau:*74.1% White*1.7% Black*1.5% Native American*1.1% Asian*0.1% Native Hawaiian or Pacific Islander*3.0% Two or more races*18.5% Other races*65.7% Hispanic or Latino -2000:...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, United States
Southwestern United States
The Southwestern United States is a region defined in different ways by different sources. Broad definitions include nearly a quarter of the United States, including Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas and Utah...
. The range is located east of the Rio Grande
Rio Grande
The Rio Grande is a river that flows from southwestern Colorado in the United States to the Gulf of Mexico. Along the way it forms part of the Mexico – United States border. Its length varies as its course changes...
and Caballo Lake
Caballo Lake
Caballo Lake is a reservoir on the Rio Grande River in southern New Mexico, United States. It is the fourth largest reservoir in New Mexico in terms of surface area and the fifth largest body of water in New Mexico in terms of volume...
, and west of the Jornada del Muerto
Jornada del Muerto
The Jornada del Muerto in the U.S. state of New Mexico was the name given by the Spanish conquistadors to the Jornada del Muerto Desert basin, and the particularly dry stretch of a route through it.The trail lead northward from central Spanish colonial New Spain, present-day Mexico, to the farthest...
; the south of the range extends into northwest Doña Ana County. The nearest towns are Truth or Consequences
Truth or Consequences
Truth or Consequences is an American quiz show originally hosted on NBC radio by Ralph Edwards and later on television by Edwards , Jack Bailey , Bob Barker , Bob Hilton and Larry Anderson . The television show ran on CBS, NBC and also in syndication...
and Hatch
Hatch, New Mexico
Hatch is a village in Doña Ana County, New Mexico, United States. The population was 1,673 at the 2000 census. It is part of the Las Cruces Metropolitan Statistical Area. The town is experiencing moderate growth, along with its outliers of Salem, Arrey, Derry, and Rincon...
.
Most of the Caballo Mountains are located on land owned by the Bureau of Land Management
Bureau of Land Management
The Bureau of Land Management is an agency within the United States Department of the Interior which administers America's public lands, totaling approximately , or one-eighth of the landmass of the country. The BLM also manages of subsurface mineral estate underlying federal, state and private...
. The mountains are unusual, and perhaps unique in New Mexico, for the relatively complete geologic history revealed by their rocks. Vehicular access to the range is by Interstate 25
Interstate 25
Interstate 25 is an Interstate Highway in the western United States. It is primarily a north–south highway. I-25 stretches from Interstate 10 at Las Cruces, New Mexico, , to Interstate 90 in Buffalo, Wyoming, .Interstate 25 is the main north–south expressway through...
from the west, by New Mexico State Road 51 from the north, and by several dirt roads from the east.
Geography
The Caballo Mountains trend north and south, with a length of approximately 32 miles (50 km). The width of the range varies from 3–6 miles (5–10 km). The highest point on the range, Timber Mountain (7,565 feet), has a topographic prominenceTopographic prominence
In topography, prominence, also known as autonomous height, relative height, shoulder drop , or prime factor , categorizes the height of the mountain's or hill's summit by the elevation between it and the lowest contour line encircling it and no higher summit...
of approximately 3,400 feet.
The types, sizes, and profiles of the Caballo watersheds vary significantly according to the part of the range that they drain. No perennial streams flow through the mountains, although the course of the Rio Grande is close to the north, west, and south margins of the range. The northern part of the Caballos drains into the Rio Grande through Ash Canyon and Mescal Canyon. The confluences of those two intermittent streams are just below Elephant Butte Dam
Elephant Butte Dam
Elephant Butte Dam or Elephant Butte Dike is a concrete gravity dam on the Rio Grande near Truth or Consequences, New Mexico. The river was dammed here, impounding the Elephant Butte Reservoir for recreation and agriculture, lessening the downstream flow from a Rio Bravo to a stream a foot deep.The...
. Water falling on the precipitous west face of the range drains directly into the Rio Grande by means of numerous first order canyons with high gradients. All are ephemeral
Ephemeral
Ephemeral things are transitory, existing only briefly. Typically the term is used to describe objects found in nature, although it can describe a wide range of things....
and less than 3 miles in length.
In contrast, the eastern side has only two primary drainages, each with a much lower gradient than those to the north and west. Water falling on the southern half of the east side flows into Barbee Draw. After joining another tributary near Point of Rocks to form Rincon Arroyo, this ephemeral drainage flows southward before joining the Rio Grande near Rincon, New Mexico
Rincon, New Mexico
Rincon is a census-designated place in Doña Ana County, New Mexico, in the United States. As of the 2000 census, the CDP population was 220...
. The length of this drainage is over 25 miles. The north portion of the east side is drained by Jornada Draw. This drainage, however, is endorheic
Endorheic
An endorheic basin is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans...
and has no surface connection to the Rio Grande.
Geology
The geological importance of the Caballo Mountains lies in the variety and scope of their exposed rocks. Geologists can assess exposed rock formations in several ways. Relative datingRelative dating
Relative dating is the science determining the relative order of past events, without necessarily determining their absolute age.In geology rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another...
compares the formation's bedding location in comparison with other formations nearby. This allows not only the identification of the older and younger formations, but conclusions about unusual local conditions, such as folding
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
, a fault displacement, or an unconformity
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
. Absolute dating
Absolute dating
Absolute dating is the process of determining an approximate computed age in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty and precision...
measures the presence and ratios of chemicals within the rocks to determine the number of years since they were deposited. The conditions existing when the rock was deposited can be determined by examining its type (igneous, metamorphic, or sedimentary), the orientation and size of crystals or sediments within it, and the orientation of the formation within its larger regional setting. By studying plant and animal fossils that may exist in the formation, it may be possible to determine not only its relative age, but the climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
at the time of deposition.
Weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
and erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
remove any rock that is exposed at the surface of the Earth. Consequently, there are no sites where all rocks deposited at that location have been preserved. Certain sites, however, may have more complete geological histories because of differences in the timing and circumstances of rock removal. The Caballo Mountains are essentially unique in New Mexico because their section of exposed rocks begins in Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
time, and runs through every geological period of the Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
eon with the exceptions of the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
and Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
. This provides an unparalleled picture of the geological history of southern New Mexico.
Stratigraphy
The basement rocks of the Caballos include plutons of graniteGranite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
, and metamorphic amphibolite
Amphibolite
Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...
and gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
. These rocks date from the Early to Middle Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
, and are found along the base of the larger fault blocks.
Throughout the early and middle Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
southern New Mexico alternated between being flooded by shallow tropical seas, and being exposed to erosion. Sedimentary deposits of early and middle Paleozoic age include:
- Bliss Formation of arkosic sandstoneSandstoneSandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
and siltstoneSiltstoneSiltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
(CambrianCambrianThe Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
to OrdovicianOrdovicianThe Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
). - El Paso Formation of dolomitesDolomitesThe Dolomites are a mountain range located in north-eastern Italy. It is a part of Southern Limestone Alps and extends from the River Adige in the west to the Piave Valley in the east. The northern and southern borders are defined by the Puster Valley and the Sugana Valley...
and limestones (OrdovicianOrdovicianThe Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
) - Montoya Formation of dolomites and cherty dolomites (OrdovicianOrdovicianThe Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
) - Fusselman Dolomite (SilurianSilurianThe Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
) - Percha ShaleShaleShale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
(DevonianDevonianThe Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
) - Lake Valley Formation of limestones and cherty limestones (Mississippian)
An unconformity
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
exists above the Lake Valley Formation, and appears to include the middle Mississippian through the early Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
periods. During the Pennsylvanian and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
periods, a major deformation created a series of uplifts and intermontane basins. This event is often referred to as the Ancestral Rocky Mountains. Associated with this event is the Magdalena Group, which includes deposits of both marine and non-marine sources. The thickness of these strata is greater than that of all earlier Paleozoic rocks. Above the Magdalena Group is the Red House Formation of packstone and shale, the Nakaye Formation of limestone, the Bar B Formation of interbedded limestone, dolomite, shale, and conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
, and the red shale beds of the Abo Formation. All of those strata are Pennsylvanian in age. Above them is thePermian Yeso Formation, which consists of sandstones, siltstone-dolomites, and limestones. The Paleozoic strata are completed by the Meseta Blanca Sandstone.
Most of the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
rocks are missing from the Caballo geological history. A second unconformity lies above the Meseta Blanca Sandstone, and includes all of the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
and Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
periods. The next oldest rocks are of Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
age and include:
- Dakota Sandstone
- Rio Salado Tongue Member of Mancos Shale
- Tres Hermanos Formation of sandstones
- Cross Tongue Member of Mancos Shale
- Gallup Sandstone
- Crevasse Canyon Formation of sandstones and mudstones
- McRae Formation of sandstones, tuffTuffTuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
, and conglomerateConglomerate (geology)A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
The Mesozoic rocks terminate below another unconformity. Above that is the Love Ranch Formation of conglomerate, mudstone and sandstone, which was deposited in the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
to early Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
. During the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, a wave of arc volcanism was felt across southern New Mexico. In the Caballo Mountains, this can be seen in the Palm Park Formation, a thick layer of andesitic or tuffaceous mudstones, sandstones, and breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
. Next is the Bell Top Formation, which consists of rhyolite
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
, basalt flows, and tuffaceous sandstones. In the southern part of the Caballo Mountains, there are remnants of a region wide sheet of flood basalts and andesite, which was laid during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
. Of similar age is the Thurman Formation of white sandstone. The Santa Fe Group was deposited during the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
and Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
.This thick layer consists of the Hayner Ranch Formation (conglomerate, sandstone and shale), the Rincon Valley Formation (conglomerate, sandstone, and mudstone), the Selden basalts, and the Camp Rice/Palomas Formations (ash fall deposits, basalts, and pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
-clast conglomerates). Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
and Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
deposits consist of alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
. On the west side of the range along the Rio Grande, the alluvial fill consists of unconsolidated fluvial
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
deposits of boulders, cobble
Cobble (geology)
A cobble is a clast of rock with a particle size of to based on the Krumbein phi scale of sedimentology. Cobbles are generally considered to be larger than pebbles and smaller than boulders . A rock made predominantly of cobbles is termed a conglomerate....
, and gravel. In the closed basin on the east side of the range, there are relatively few fluvial deposits. Instead, the sediment includes a flat, thin veneer of sand and gravel.
Tectonics
The Rio Grande Rift is a continental rift zone, which extends approximately 680 miles (~1,100 km) from central ColoradoColorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
in the north to the state of Chihuahua, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
in the south. It is the product of extensional
Extensional
In philosophy of language, a context in which a sub-sentential expression e appears is called extensional if and only if e can be replaced by an expression with the same extension and necessarily preserve truth-value. The extension of a term is the set of objects that that term denotes.Take the...
tectonic (or divergent) forces that formed a series of basins between the Colorado Plateau
Colorado Plateau
The Colorado Plateau, also called the Colorado Plateau Province, is a physiographic region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. The province covers an area of 337,000 km2 within western Colorado, northwestern New Mexico,...
and the North American craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
Thin continental crust
Crust
Crust may refer to:* Crust * The Crust, television seriesPhysical sciences:* Crust , at least continent-wide structure* Soil crust, local biology-sensitive structureFood:* Crust, dense surface layer of bread...
, normal fault block topography, high regional elevation, and volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
is found over the course of the rift.
The history of movement along the rift has been divided into three separate stages: an initial stage during the late Eocene to early Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, a second stage during the late Oligocene to late Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
, and a third stage beginning in the late Miocene or early Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
and continuing to the recent past. Activity in the vicinity of the Caballos during the first stage included explosive rhyolitic eruptions from cauldrons located to the northwest, west, and southeast. The earliest eruptions took place in the Dona Ana Mountains
Doña Ana Mountains
The Doña Ana Mountains are a mountain range in Doña Ana County, New Mexico....
and Organ Mountains
Organ Mountains
The Organ Mountains are a rugged mountain range in southern New Mexico in the Southwestern United States. They lie east of the city of Las Cruces, in Doña Ana County.-Geography:...
between 36.2 and 35.4 Ma. The Emory cauldron, located in the Black Range
Black Range
The Black Range is an igneous mountain range running north-south in Sierra and Grant counties in west-central New Mexico, in the southwestern United States. Its central ridge forms the western and eastern borders, respectively, of the two counties through much of their contact...
, was active approximately 34.9 Ma. What is now the San Mateo Mountains (Socorro County)
San Mateo Mountains (Socorro County, New Mexico)
The San Mateo Mountains are a small mountain range in Socorro County, in west-central New Mexico in the southwestern United States. The highest point in the range is West Blue Mountain, at 10,336 ft . The range runs roughly north-south and is about 40 miles long...
contained at least two cauldrons, the Nogal Canyon cauldron (28.6 Ma) and the Mount Withington cauldron (27.4 Ma). Local subsiding appears to have begun around 34.9 Ma. The Caballo Mountains began to rise in the late Oligocene, and throughout the Miocene. Approximately 9.6 Ma, the eruption of basalts near Fort Selden
Fort Selden
Fort Selden was a United States Army post, occupying the area in what is now Radium Springs, New Mexico. Established in 1865 for the purpose of protecting westward settlers from Native American raids, the post fell into disrepair after the American Civil War...
signaled the renewal of crustal extension and volcanism in the southern part of the rift. Activity along both older and new faults increased the number, but decreased the width of basins along this portion of the rift.
Economic Geology
The Caballo Mountains have few large intrusives, and as a result, hydrothermal mineralization is not extensive. Nevertheless, prospecting in the range began in about 1883, and several mines opened in the first decade of the 20th century. Production has been concentrated in three areas:- Northern Red Hills - fluorspar
- Palomas Gap - copper, vanadium, lead, and fluorspar
- Southern Caballos - gold, fluorspar, barite, and manganese
It has been estimated that the total value of copper, silver, gold, and lead produced from the Caballos before 1952 did not exceed $200,000. At present, more fluorspar is produced than any other mineral. The largest fluorspar deposits are found in Precambrian granite, and jasperized Fusselman Dolomite.
Ecology
As is the case with many other mountain ranges in southern New Mexico, the Caballo Mountains impose extreme demands on ecological communities. With the exception of the intermittent streams in the northern part of the range, and the area in close proximity to the Rio Grande, there is very little permanent water. Precipitation quickly evaporates, runs off, or soaks into the ground, leaving little for plants or animals. Consequently, water management is a critical factor for both plants and animals.Soils on the mountains are generally rocky and thin.
Plant communities can be generally characterized as Chihuahuan desert scrublands, creosotebush desert, and desert grasslands. Dominant shrub species include creosote bush
Creosote bush
Larrea tridentata is known as Creosote bush as a plant, chaparral as a medicinal herb, and as "gobernadora" in Mexico, Spanish for "governess," due to its ability for inhibiting the growth of nearby plants to have more water. In Sonora, it is more commonly called "hediondilla." It is a flowering...
(Larrea tridentata), honey mesquite
Honey Mesquite
Prosopis glandulosa, commonly known as honey mesquite, is a species of small to medium-sized flowering tree in the legume family, Fabaceae. It is native to the Southwestern United States and Mexico, growing as far north as southern Kansas and as far east as the eastern fifth of Texas, where...
(Prosopis glandulosa), soaptree yucca
Soaptree yucca
The Soaptree yucca is a perennial plant in the genus Yucca. It is native to southwestern North America, in the Sonoran Desert and Chihuahuan Desert in the United States , and northern Mexico .This plant grows from 1.2-4.5 m tall, with a sparsely branched trunk...
(Yucca elata), and four winged saltbush (Atriplex canescens
Atriplex canescens
Atriplex canescens, Chamiso, Chamiza, Four wing saltbush, Four-wing saltbush, and Fourwing saltbush, is a species of evergreen shrub in the Amaranthaceae family, which is native to the western and mid-western United States....
). Common grasses include black grama
Black grama
Bouteloua eriopoda, commonly known as Black Grama, is a perennial prairie grass that is native to the Southwestern United States. Its main means of reproduction is by stolons, as its ratio of viable seeds to sterile ones is naturally low. The disparity may play a role in its lack of tolerance to...
(Bouteloua eriopoda), blue grama
Blue grama
Blue Grama, Bouteloua gracilis, is a long-lived, warm season, C4 perennial grass native to North America. It is most commonly found from Alberta east to Manitoba and south across the Rocky Mountains, Great Plains, and Midwest states to Mexico...
(Bouteloua gracilis), sideoats grama
Sideoats grama
Bouteloua curtipendula, commonly known as sideoats grama, is a perennial, short prairie grass that is native throughout the temperate and tropical Western Hemisphere, from Canada south to Argentina.-Description:...
(Bouteloua curtipendula), and alkali sacaton (Sporobolus airoides
Sporobolus airoides
Sporobolus airoides is a species of grass known by the common name alkali sacaton. It is native to western North America, including the Western United States west of the Mississippi River, British Columbia and Alberta in Canada, and northern and central Mexico...
).
The most common mammalian predators are mountain lions (Felis concolor) and coyotes (Canis latrans). Other common mammals are Black-tailed jackrabbit
Black-tailed Jackrabbit
The black-tailed jackrabbit , also known as the american desert hare, is a common hare of the western United States and Mexico, where it is found at elevations from sea level to up to...
(Lepus californicus), desert cottontail
Desert Cottontail
The Desert Cottontail , also known as Audubon's Cottontail, is a New World cottontail rabbit, a member of the family Leporidae....
, (Sylvilagus auduboni) and kangaroo rats (Dipodomys merriami and Dipodomys spectabilis).
Common birds of prey include golden eagles (Aquila chrysaetos), Swainson's hawk
Swainson's Hawk
The Swainson's Hawk , is a large buteo hawk of the Falconiformes, sometimes separated in the Accipitriformes like its relatives. This species was named after William Swainson, a British naturalist...
(Buteo swainsoni), Northern harrier (Circus cyaneus), and burrowing owl
Burrowing Owl
The Burrowing Owl is a tiny but long-legged owl found throughout open landscapes of North and South America. Burrowing Owls can be found in grasslands, rangelands, agricultural areas, deserts, or any other open dry area with low vegetation. They nest and roost in burrows, such as those excavated...
(Athene cunicularia). Other birds include roadrunner
Roadrunner
Roadrunners are birds of the genus Geococcyx.Roadrunner or Road Runner may also refer to:* Wile E. Coyote and Road Runner, an animated character based on the bird** The Road Runner Show, compiled cartoons including the character...
(Geococcyx californianus), quail
Quail
Quail is a collective name for several genera of mid-sized birds generally considered in the order Galliformes. Old World quail are found in the family Phasianidae, while New World quail are found in the family Odontophoridae...
(Callipepla gambelii and Callipepla squamata), doves
Doves
Doves are an English alternative indie rock band, originating from Wilmslow, Cheshire. The band comprises brothers Jez Williams and Andy Williams , and Jimi Goodwin . The members started working seriously together after meeting at The Haçienda in Manchester. Doves' unofficial fourth member is...
(Zenaida macroura and Zenaida asiatica).
Common reptiles include Collared lizards
Crotaphytidae
The family Crotaphytidae, or collared lizards, are desert-dwelling reptiles native to the southwest USA and northern Mexico. They are very fast-moving animals, with long limbs and tails, and are carnivorous, feeding mainly on insects....
(Crotaphytus collaris), Roundtail Horned Lizard
Roundtail Horned Lizard
The roundtail horned lizard is one of the smaller species of horned lizard. Their specific epithet is from the Latin word modestum meaning modest or calm...
(Phrynosoma modestum), Striped whipsnake
Striped Whipsnake
The Striped Whipsnake is a species of nonvenomous colubrid snake that is closely related to the California Whipsnake . It is native to the western United States and northern Mexico....
(Masticophis taeniatus), and Western diamondback rattlesnake (Crotalus atrox
Crotalus atrox
Crotalus atrox, the "western diamondback rattlesnake", is a venomous rattlesnake species found in the United States and Mexico. It is likely responsible for the majority of snakebite fatalities in northern Mexico and the second greatest number in the USA after C. adamanteus. No subspecies are...
).