The Geste Formation has provided a faunal assemblage of vertebrates unique for the Argentine Northwest, with several groups of mammals, most notably the only Paleogene interatheres of northwestern Argentina, reptiles and frogs.

[2] The most extensive outcrops of the formation occur between three volcanoes in the area; the Tebenquicho in the west, Cerro Ratones in the east and Hombre Muerto to the southeast.

[2] In the Pastos Grandes Basin, in outcrops located on the eastern flank of the Sierra de Copalayo in Salta Province, the Geste Formation was divided by Alonso (1992) into three members: lower, middle, and upper.

[2] The paleoclimate of the time was much more humid than today, with elevated temperatures compared to the present-day climate and the area was at lower altitudes before the final phase of the Andean orogeny which did not take place before the Miocene.

[7] The faunal assemblage comprises mammals of various groups, with notoungulates and armadillos dominating, reptiles (crocodiles, turtles and snakes not assigned to specific genera) and frog fossils.