The Chama Basin is a geologic

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 ...

located 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 ...

. The basin closely corresponds to the

drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...

of the

Rio Chama The Rio Chama, a major tributary river of the Rio Grande, is located in the U.S. states of Colorado and New Mexico. The river is about long altogether. From its source to El Vado Dam its length is about , from El Vado Dam to Abiquiu Dam is abou ...

and is located between the eastern margin of the

San Juan Basin The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah ...

and the western margin 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 ...

. Exposed in the basin is a thick and nearly level section of

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particle ...

Permian The Permian ( ) is a geologic period and 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 251.9 Mya. It is the last period of the Pale ...

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

age, with some younger overlying

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcan ...

. The basin has an area of about .

Stratigraphy

In stratigraphic order (youngest to oldest), the

stratigraphic units A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize ...

of the Chama Basin are: :

:: Graneros Shale Member,

Mancos Shale The Mancos Shale or Mancos Group is a Late Cretaceous (Upper Cretaceous) geologic formation of the Western United States. The Mancos Shale was first described by Cross and Purington in 1899 and was named for exposures near the town of Mancos ...

::Twowells Sandstone Tongue,

Dakota Formation The Dakota is a sedimentary rock, sedimentary geologic unit name of Formation (stratigraphy), formation and Group (stratigraphy), group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and ...

:: Whitewater Arroyo Shale Tongue, Mancos Shale :: Paguate Sandstone Tongue, Dakota Formation :: Clay Mesa Shale Tongue, Mancos Shale ::Cubero Sandstone Tongue, Dakota Formation ::Oak Canyon Member, Dakota Formation ::Encinal Canyon Member, Dakota Formation :

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 Mya. The J ...

Burro Canyon Formation The Burro Canyon Formation is an Early Cretaceous Period sedimentary geologic formation, found in western Colorado, the Chama Basin and eastern San Juan Basin of northern New Mexico, and in eastern Utah, US. Description The lithology of t ...

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, ...

:: Bluff Sandstone ::

Summerville Formation The Summerville Formation is a geological formation in New Mexico, Colorado, and Utah of the Southwestern United States. It dates back to the Oxfordian stage of the Late Jurassic.Wilcox 2007 Description The formation consists of up to of red ...

Todilto Formation The Todilto Formation is a geologic formation in northern New Mexico and southeastern Colorado. It preserves fossils dating back to the Callovian stage of the middle Jurassic period. Description The formation consists of evaporites. It is di ...

Entrada Sandstone The Entrada Sandstone is a formation in the San Rafael Group found in the U.S. states of Wyoming, Colorado, northwest New Mexico, northeast Arizona, and southeast Utah. Part of the Colorado Plateau, this formation was deposited during the Jurass ...

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

Chinle Group The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...

:::

Rock Point Formation The Rock Point Formation is a geologic formation in New Mexico, Arizona, and Utah. It preserves fossils dating back to the late Triassic. Description The formation is up to 70 m thick and is mostly reddish-brown and grayish-red massive siltstone ...

:::

Petrified Forest Formation The Petrified Forest Member is a stratigraphic unit of the Chinle Formation in Arizona, Colorado, New Mexico, Nevada, and Utah. It preserves fossils dating back to the Triassic period. Subunits Beds (are in alphabetical order, asterisks ...

:::

Poleo Formation The Poleo Formation is a geologic formation in northern New Mexico. Its stratigraphic position corresponds to the late Triassic epoch. Description The Poleo Formation is a cliff-forming formation composed mostly of yellowish-gray fine to medium ...

:::

Salitral Formation The Salitral Formation is a Late Triassic geologic formation found in north-central New Mexico, primarily the northwestern Jemez Mountains. It is an older subunit of the Chinle Group (or formation), overlying the Shinarump Conglomerate and under ...

:::

Shinarump Formation The Shinarump Conglomerate is a geologic formation found in the Four Corners region of the United States. It was deposited in the early part of the Late Triassic period. Description The Shinarump Conglomerate is a highly resistant coarse-grained ...

:::

Zuni Mountains Formation The Shinarump Conglomerate is a geologic formation found in the Four Corners region of the United States. It was deposited in the early part of the Late Triassic period. Description The Shinarump Conglomerate is a highly resistant coarse-grained ...

:Permian ::

Cutler Group The Cutler Formation or Cutler Group is a rock unit that is exposed across the U.S. states of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. It was laid down in the Early Permian during the Wolfcampian epoch. Descri ...

:::

Arroyo del Agua Formation The Arroyo del Agua Formation is a Formation (geology), geologic formation in New Mexico. It preserves fossils dating back to the early Permian Period (geology), period. Description The Arroyo del Agua Formation consists of siliclastic red beds ...

:::

El Cobre Canyon Formation The El Cobre Canyon Formation is a geologic formation in New Mexico. It preserves fossils dating back to the late Pennsylvanian to early Permian periods. Description The El Cobre Canyon Formation consists of siliciclastic red beds with a total ...

Fossil quarries

The basin is rich in fossil quarries. Its potential was first recognized by

John Strong Newberry John Strong Newberry (December 22, 1822 – December 7, 1892) was an American physician, geologist and paleontologist. He participated as a naturalist and surgeon on three expeditions to explore and survey the western United States. During the C ...

, who visited the basin in 1859 as part of the Macomb Expedition. Newberry visited the copper mines of El Cobre Canyon and identified Triassic plant leaves. The basin was subsequently visited by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy intereste ...

in 1874 during the

Wheeler Survey The Wheeler Survey, carried out in 1872-1879, was one of the "Four Great Surveys" conducted by the US government after the Civil War primarily to document the geology and natural resources of the American West. Supervised by First Lieutenant (lat ...

, David Baldwin collected from sites in the Arroyo del Agua area for five field seasons between 1877 and 1881, working first for

O.C. Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale University, Yale College and National Academy of Sciences, President of the National Academy of Sciences. He was one of the preeminent s ...

and later for Cope, who was Marsh's bitter rival. The Baldwin bonebed yielded the first Permian vertebrates discovered in New Mexico. However, Baldwin failed to elicit much interest from either Marsh or Cope. The famous Whitaker quarry of

Ghost Ranch Ghost Ranch is a retreat and education center located close to the village of Abiquiú in Rio Arriba County in north central New Mexico, United States. It was the home and studio of Georgia O'Keeffe, as well as the subject of many of her pain ...

, New Mexico, also been referred to as the ''Coelophysis'' quarry due to preserving a large number of specimens of the early

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

Coelophysis bauri ''Coelophysis'' ( traditionally; or , as heard more commonly in recent decades) is an extinct genus of coelophysid theropod dinosaur that lived approximately 228 to 201.3 million years ago during the latter part of the Triassic Period fro ...

'', was one of the most important of the basin. Even richer is the Snyder quarry, discovered in 1998.

References

{{coord, 36.64, -106.69, display=title, region:US-NM Structural basins of the United States Cenozoic New Mexico Colorado Plateau