[4] The mammal assemblage of the Cerro Azul-Epecuén unit is the most diverse for the Huayquerian Late Miocene age, possibly ranging into the Pliocene.

They are composed of silts, sandy silts and very thin silty sands, reddish and brown colored, with a homogeneous and compact general aspect, and frequent carbonate nodules and evidences of pedogenic processes.

Visconti et al. (2010) interpreted them as eolian deposits characterized by loessic materials, with a high percentage of lithic fragments and volcaniclastic sediments.

[9] The sediments and their fauna belong to a sedimentary and faunal cycle, which followed the withdrawal (around 10 Ma) of a widespread marine transgression that extended from central Argentina, to western Uruguay and southern Paraguay and Brazil, the "Paraná Sea" or mar paranense in Spanish.

[10] Large cylindrical sediment-filled structures, 115 of which interpreted as mammal burrows occur within the loess-paleosol sequence of the formation.