The Espanola basin is a

structural basin A structural basin is a large-scale structural formation of rock strata formed by tectonic warping of previously flat-lying strata. They are geological depressions, the inverse of domes. Elongated structural basins are also known as synclines ...

in northern

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

. It is located in the

Rio Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio ...

watershed and is part of the

Rio Grande rift The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihu ...

. The definition of its boundaries is not fully settled, but the basin is usually defined such that it includes the cities of Santa Fe, Los Alamos, and Espanola.

Geology

The basin is part of the

, a north-south sequence of structural basins that have developed where

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

forces have pulled the

Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area ...

away from the interior of North America. The basin is partially filled with sediments eroded from the higher ground to the east and west or brought in by the ancestral Rio Grande. The Jemez volcanic field is located on the western margin of the basin and has contributed additional volcanic sediments to the basin. The sediments formed the

Tesuque Formation The Tesuque Formation is a geologic formation in north-central New Mexico, United States. The formation provides an unusually complete record of the evolution of mammals during the Miocene epoch. Description The formation is primarily siltstone ...

and Chamita Formation of the

Santa Fe Group The EAC Invest A/S, formerly known as the Santa Fe Group and East Asiatic Company ( da, italic=yes, Det Østasiatiske Kompagni or ''ØK'') is a multinational holding and investment company, based in Copenhagen, Denmark. History The East Asiat ...

. The basin began forming during the middle to late

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but ...

, around 25 million years ago. The early basin was more extensive than the present basin, and there is no evidence of boundary faults at this stage of development. The basin was likely a shallow depression between the

Sierra Nacimiento The Sierra Nacimiento (official name), or Nacimiento Mountains, are a mountain range in the northwestern part of the U.S. state of New Mexico. They are just west of the more prominent Jemez Mountains near the town of Cuba, and are separated ...

to the west and the

Sangre de Cristo Mountains The Sangre de Cristo Mountains ( Spanish for "Blood of Christ") are the southernmost subrange of the Rocky Mountains. They are located in southern Colorado and northern New Mexico in the United States. The mountains run from Poncha Pass in South ...

to the east. Faulting and volcanism began on the west side of the basin in mid-Miocene time, around 14 million years ago. In the early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Jemez Mountains The Jemez Mountains are a group of mountains in Rio Arriba, Sandoval, and Los Alamos counties, New Mexico, United States. Numerous Puebloan Indian tribes have lived in the Jemez Mountains region since before the Spanish arrived in New Mexico. ...

. The basin is an asymmetric

half-graben A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults. Rift and fault structure A rift is a region where the lithosphe ...

, with the beds within the basin dipping to the west. No major bounding faults are found on the east side of the basin. The accumulated sediments in the center of the basin are about 2 to 3 km thick, becoming thinner to the east and pinching out against the

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, 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 th ...

rock of the Sangre de Cristo Mountains. At greater depths near the basin center, there is are thick beds of older sedimentary rock that may be an old lake deposit of the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

Galisteo or El Rito Formations. The deepest portion of the rift is along the Velarde graben, which is up to 5 km deep. The Rio Grande became established in the basin in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Cerros del Rio periodically dammed the river and created a large lake in the Espanola basin.

Fossils

The Espanola basin has yielded vertebrate fossils since the 1870s, which provide the most extensive

Miocene The Miocene ( ) is the first 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 means "less recent" ...

fossil record in New Mexico. Most of the fossils are mammals, but lizard and turtle fossils have also been recovered, along with freshwater diatoms.

Economic resources

The sediments beneath the basin form a major regional

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteri ...

supplying water to most residents of the basin. This aquifer is under stress from urban development and drought and the basin has been heavily studied to permit better management of this resource. Geophysical measurements show a deep layer of sedimentary rock in the basin, and this has been the target of exploratory drilling for

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

. However, the beds were found to most likely be relatively young (Eocene) lake sediments rather than the petroleum-bearing

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

beds that were hoped for.

References

{{geology-stub Geology of New Mexico Sedimentary basins of North America