The upper Santa Fe Group was deposited after integration of these basins into the ancestral Rio Grande, so that their drainage flowed toward southern New Mexico.

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.

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.

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

[15] Fossils found in the Santa Fe Group include the hemicyonid Hemicyon and the borophagine canid Carpocyon webbi, the antilocaprids Cosoryx, Merycodus, and Ramoceros, chiroptera from the Vespertilionidae and Antrozoinae, the turtle Glyptemys valentinensis, and mastodonts.

He likened these to the badlands of South Dakota and correctly determined that they were upper Tertiary in age and were much younger than the Galisteo Formation beds which they overlie.

[18] The formation was promoted to group rank in 1953[24] and defined by Baldwin three years later as basin-filling sedimentary and volcanic rocks of the Rio Grande rift.