The formation is primarily siltstone and fine sandstone, with some boulder conglomerate beds in its eastern exposures close to the Sangre de Cristo Mountains.

[2] The Nambe Member is pinkish to reddish coarse-grained alluvial fan deposits resting on basement rock of the Sangre de Cristo Mountains.

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.

[14] G.K. Gilbert visited San Ildefonso Pueblo with the Hayden Survey in 1873 and found fossil mammal bones characteristic of the Pliocene.

Marsh's bitter rival, Edward Drinker Cope, arrived at San Ildefonso the next year and collected a number of Miocene reptile, bird, and mammal fossils.

[15] 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 (merged with the Department of Vertebrate Paleontology of the American Museum of Natural History in 1968) carried out field work through 1972.

[16] Most of the fossils came from the Pojoaque Member of the Tesuque Formation and were almost entirely found within thin (0.5–3 m) maroon-red to pale green claystone to fine-grained siltstone beds of lithosome B.

[17] Fossils found in the Tesuque Formation include the canids Hemicyon and Carpocyon webbi, the antilocaprids Cosoryx, Merycodus, and Ramoceros, chiroptera from the Vespertilionidae and Antrozoinae, the turtles Glyptemys valentinensis and Kinosternon pojoaque,[18] and mastodonts.

[21] 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.