The formation is primarily siltstone and fine sandstone, with some boulder conglomerate beds in eastern exposures close to the Sangre de Cristo Mountains. It is interpreted as coalesced alluvial fans with highly variable lithology. There is significant crossbedding and lenticular bedding, and some sandstone beds are well cemented with calcite. The formation dips 10 degrees to the west. Faulting makes an accurate estimate of its thickness uncertain, and it was originally estimated to be over thick. However, a careful reconstruction taking into account faults gives a thickness of. The Nambe Member is pinkish to reddish coarse-grained alluvial fan deposits resting on basement rock of the Sangre de Cristo Mountains. The member is named for Nambé Pueblo and has a total thickness of about. The Skull Ridge Member is separated from the Nambe Member by a distinctive ash bed. The member has numerous other ash beds, which result in relatively strong cementing that makes this a cliff-forming member. The upper portion is much less resistant to erosion. The member is up to thick. Galusha and Blick did not identify the geographical location for which the member was named, and the place name "Skull Ridge" is unknown in New Mexico. The Pojoaque Member is separated from the Skull Ridge Member by a greenish-gray conglomerate bed interpreted as lag gravel on an erosional surface. It is named for the Pojoaque Bluffs, also known as Los Barrancos. The formation disappears into the subsurface under the Rio Grande River floodplain but is at least thick. The Chama-El Rito Member is found only in the northwestern portion of the Chama Basin. It correlates with the Skull Ridge and Pojoaque Members, but contains conglomerate lenses with distinctive volcanic clasts likely derived from the San Juan volcanic field. The Ojo Caliente Member is of soft eolian sandstone overlying the Chama-El Rito member. It is named for the village of Ojo Caliente. In addition to the traditional lithostratic units, the Tesuque Formation is divided into two lithosomes. Lithosome A is granitic material deposited by a network of westward-flowing streams off the Sangre de Cristo Mountains. Lithosome B is richer in clay and Paleozoic clasts and was deposited by south- to southwest-flowing rivers coming from the Penasco area. The two can be distinguished in the field by the redder coloration of Lithosome A compared with the tan to gray color of Lithosome B.
Fossils
visited San Ildefonso Pueblo with the Hayden Survey in 1873 and found fossil mammal bones characteristic of the Pliocene. Some of these were sent to Othniel Marsh. His bitter rival, Edward Drinker Cope, arrived at San Ildefonso the next year and collected a number of Miocene repile, bird, and mammal fossils. Childs Frick sent an expedition into the Tesuque area in 1924, and immediately recognized the paleontological potential of the Santa Fe beds. The Fricks Laboratory carried out field work through 1972. Work prior to 1940 was careless about identifying exact source strata, though greater care was taken threafter. Most of the fossils came from the Pojoaque Member of the Tesuque Formation and were almost entirely found within thin maroon-red to pale green claystone to fine-grained siltstone beds of lithosome B. These are interpreted as small lacustrine deposits. Fossils found in the Tesuque Formation include the canids Hemicyon and Carpocyon webbi, the antilocapridsCosoryx, Merycodus, and Ramoceros, chiroptera from the Vespertilionidae and Antrozoinae, the turtleGlyptemys valentinensis, and mastodonts.
History of investigation
The beds making up the unit were originally described by Bryan and McCann in 1937 as the Middle Red member of the Santa Fe Formation. The formation was named by Baldwin in 1956 at the same time that the Santa Fe Formation was promoted to group status. The formation is named after exposures around the town of Tesuque, New Mexico. In 1971, Galusha and Blick removed the uppermost beds from the Tesuque Formation as the Chamita Formation and divided the Tesuque Formation into members. These were, in ascending stratigraphic order, the Skull Ridge Member, the Nambe Member, Pojoaque Member, the Chama-El Rito Member, and the Ojo Caliente Member.the Manley added the Cejita Member in 1977.
