The Coyote Mountains are a small mountain range in

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

and Imperial County in

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...

.''El Cajun, California,'' 30x60 Minute Topographic Quanrangle, USGS, 1979 The Coyotes form a narrow ESE trending wide range with a length of about . The southeast end turns and forms a north trending "hook". The highest point is Carrizo Mountain on the northeast end with an elevation of . Mine Peak at the northwest end of the range has an elevation of . Coyote Wash along Interstate 8 along the southeast margin of the range is 100 to 300 feet in elevation. Plaster City lies in the

Yuha Desert The Yuha Desert is a section of the Sonoran Desert located in the Imperial Valley of California, south of Interstate 8, west of El Centro, and north of the international border. Unique aspects of the Yuha Desert include the Oyster Shell Beds, ...

about east of the east end of the range.''Carrizo Mountain, California,'' 15 Minute Topographic Quadrangle, USGS, 1959''Plaster City, California,'' 15 Minute Topographic Quadrangle, USGS, 1957 To the southeast lie the

Jacumba Mountains The Jacumba Mountains are a mountain range of the Peninsular Ranges in eastern San Diego County, California, near the Mexico–United States border The international border separating Mexico and the United States extends from the Pacific O ...

and the Volcanic Hills. To the north and northeast lie the Carrizo Badlands, the Carrizo Valley and the Fish Creek Mountains. The west end of the range is within

Anza-Borrego Desert State Park Anza-Borrego Desert State Park (, ''Help:Pronunciation respelling key, AN-zə bə-RAY-goh'') is a California State Park located within the Colorado Desert of Southern California, United States. Created in 1932, the park takes its name from 18th ...

and the east end is within the Carrizo Naval Gunnery Range. The international border lies approximately south of the southeast margin of the range. The range consists of sand dunes left over from the ancient inland Sea of Cortez. Seismic activity has raised these. Much of the terrain is still loose dirt, interspersed with sandstone and occasional quartz veins. A dirt road leads towards the mountains, starting off State Highway 2 (S2), also known as the Imperial Highway, not far from the desert community of

Ocotillo ''Fouquieria splendens'', commonly known as ocotillo, is a plant indigenous to the Mojave, Sonoran, Chihuahuan and Colorado deserts in the Southwestern United States (southern California, southern Nevada, Arizona, New Mexico, Texas), and nor ...

. There are no marked trails and the footing is treacherous, made up of loose sand, dirt and crumbled shards of sandstone. Most slopes have no vegetation, but there is occasional

mesquite Mesquite is a common name for some plants in the genera ''Neltuma'' and '' Strombocarpa'', which contain over 50 species of spiny, deep-rooted leguminous shrubs and small trees. They are native to dry areas in the Americas. Until 2022, these ge ...

and

ocotillo ''Fouquieria splendens'', commonly known as ocotillo, is a plant indigenous to the Mojave, Sonoran, Chihuahuan and Colorado deserts in the Southwestern United States (southern California, southern Nevada, Arizona, New Mexico, Texas), and nor ...

, with coastal cholla at lower elevations. The local fauna includes jackrabbits and sparrows. There are a few ancient sand dunes that have been fossilized and hollowed out by winds, producing wind caves. Marine fossils such as sand dollars and snails can be found, but it is illegal to remove any fossils. In 1994, the

United States Congress The United States Congress is the legislature, legislative branch of the federal government of the United States. It is a Bicameralism, bicameral legislature, including a Lower house, lower body, the United States House of Representatives, ...

designated 18,631 acres (75 km²) as a U.S.

Bureau of Land Management The Bureau of Land Management (BLM) is an agency within the United States Department of the Interior responsible for administering federal lands, U.S. federal lands. Headquartered in Washington, D.C., the BLM oversees more than of land, or one ...

managed U.S. wilderness area, the Coyote Mountains Wilderness.

Geology

The Coyote Mountains range consists of uplifted metamorphic basement rocks overlain by younger

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

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. The peaks and mountain ranges are primarily

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 ...

and

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

basement rocks, which consist of

marble Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or Dolomite (mineral), dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is ty ...

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

, and

gneiss Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...

. This metamorphic basement rock and overlying volcanic and sedimentary rocks have been uplifted and exposed due to

seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

along the Elsinore Fault Zone.

Volcanism

During the

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 ...

, around 22-14 million years ago, volcanic activity produced various volcanic rock features including

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 ...

flows, an

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

plug, and various

volcaniclastic Volcaniclastics are geologic materials composed of broken fragments (clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...

s including

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

s and

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

s, known as the Alverson Formation. These volcanic rocks are primarily exposed along the east and southeastern portion of the range, and are best viewed and easily accessed in th
Painted Gorge
area of the range (where multiple volcanic rock types of varying colors are exhibited, giving the area a gorgeous 'painted' appearance).

Marine incursion

During the late Miocene, initiation of motion on the West Salton detachment fault caused rapid subsidence of the

Salton Trough The Salton Trough is an active tectonic pull-apart basin, or graben. It lies within the Imperial, Riverside, and San Diego counties of southeastern California and extends south of the Mexico–United States border into the state of Baja Califo ...

region, resulting in a marine incursion between 6.3 and 4.3 million years ago. This resulted in the Imperial Formation, composed of locally derived fossiliferous shallow marine sandstones and conglomerates that were deposited in a shallow inland sea across much of the Salton Trough. In the Coyote Mountains, these rocks were deposited directly on the older metamorphic and volcanic rocks. The Imperial Formation preserves many corals as well as shallow marine invertebrates and vertebrates.

Influence of the Colorado River Delta

The marine incursion of the ancestral

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 ...

also introduced a single, very large depositional system (the Colorado River delta) into the Salton Trough, which rapidly prograded to the south (Winker and Kidwell, 1986). During the early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Deguyños Formation of the Imperial Group (formerly the Imperial Formation). The Deguyños Formation represents the distal prodelta portion of the Colorado River delta, and is characterized by upward-coarsening cycles of

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

and/or

coquina Coquina () is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically sorted fragments of mollusks, trilobites, brachiopods, or other invertebrates. The term ''coquina'' comes from the S ...

shell beds. As the Colorado River depositional system evolved later in the Pliocene, between 4.2 and 2.8 million years ago, the marine deltaic phase gave way to a meandering fluvial system. Deposition of marine sedimentary deposits gradually transitioned into deposition of nonmarine, predominantly fluvial/delta front sediments of the Colorado river. In the Coyote Mountains, this is expressed by the presence of upward fining sequences of fine, light pink to pale orange sandstones and reddish-gray mudstones, known as the Arroyo Diablo Formation of the Palm Spring Group (previously the Diablo member of the Palm Spring Formation). Further deposition of locally derived sediments continued to accumulate in the area between 2.8 and ≈1 million years ago, primarily manifested by the Hueso Formation. Eventually (0.95 Ma), the tectonic regime in the area changed, and basin subsidence and accumulation of sediments ceased. Erosion in Anza-Borrego

Recent uplift

The Coyote Mountains lies within a complex tectonic region. The Salton Trough itself is a

pull-apart basin In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend create an area of crust ...

that is the result of crustal stretching and sinking by the combined actions of the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

and the

East Pacific Rise The East Pacific Rise (EPR) is a mid-ocean rise (usually termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), at a divergent tectonic plate bound ...

Tectonism Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

related to the North America – Pacific

plate boundary Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

is primarily manifested by the

, the Elsinore Fault Zone, the Imperial Fault Zone, and the San Jacinto Fault Zone, as well as a complex system of interconnecting faults. These major right lateral strike-slip faults have transformed the region in geologically recent times. Within the last ≈1.2 million years, the Elsinore Fault Zone and its associated subordinate faults are responsible for rapidly uplifting metamorphic basement rocks and overlying volcanic and sedimentary rocks of the Coyote Mountains, revealing the complex stratigraphic record of their tectonic, climatic, and paleontological evolution. Marine fossils and sedimentary deposits that once formed in a shallow sea (ancestral Gulf of California) now sit at an elevation of over 2000 feet above sea level. This rapid uplift has also accelerated and facilitated increased erosion and weathering. Wind and rain carve steep canyons into the recently exposed rocks, and transport loose material downslope. Gravels derived from this erosion form terraces as old as the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

and as recent as the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

(current epoch), which overlie all of the units in the Coyote Mountains. These terraces are further eroded and carved into by a system of active anastomosing drainages. On the north side of the Coyote Mountains, these drainages carve into the poorly

lithified Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificati ...

sediments of the Imperial and Palm Spring Groups, forming the Carrizo Badlands. These processes are ongoing and have continued throughout the past ≈1.2 million years. Sediments of the Imperial and Palm Spring Groups north of the Coyote Mountains are deformed by the recent uplift of the range. Brittle and ductile deformation of sediments in this area is consistent with prior interpretations of uplift and inversion of the Fish Creek–Vallecito basin as a result of initiation of the Elsinore and other strike-slip faults in the western Salton Trough ≈1.2 Ma (Dorsey et al., 2011). Continued right-lateral strike-slip motion on the Elsinore fault is accommodated by a network of ladder-like faults known as the Andradé ladder structure. This ≈7-km-wide fault structure is consistent with a zone of distributed right-lateral shear and rotation that accommodates the right-lateral deformation between the Elsinore and Painted Gorge faults.Smart, J.W. (2018) "Structural geology of the Eastern Carrizo Badlands, north of the Coyote Mountains, Southern California" https://csuchico-dspace.calstate.edu/handle/10211.3/211211

References

External links

Coyote Mountains Wilderness
- BLM {{Authority control Mountain ranges of the Colorado Desert Peninsular Ranges Mountain ranges of San Diego County, California Mountain ranges of Imperial County, California