The formation comprises moderately-sorted, fine to medium sandstones with angular quartz-feldspathic clasts. Conspicuous rounded green grains are probably glauconite, but berthierine cannot be dismissed. The matrix is micritic and volcanogenic, possibly bentonitic. The formation was deposited in an estuarine to mid shelf environment. Fossils of sharks, turtles and the tropical dolphin Urkudelphis were recovered from the formation.[1][2]
^Tanaka, Y.; Abella, J.; Aguirre-Fernández, G.; Gregori, M.; Fordyce, E. R. (2017). "A new tropical Oligocene dolphin from Montañita/Olón, Santa Elena, Ecuador". PLOS ONE. 12 (12): e0188380. Bibcode:2017PLoSO..1288380T. doi:10.1371/journal.pone.0188380. PMC 5737981. PMID 29261688.
^Carrillo-Briceño, J. D.; Villafaña, J. A.; De Gracia, C.; Flores-Alcívar, F. F.; Kindlimann, R.; Abella, J. (2020). "Diversity and paleoenvironmental implications of an elasmobranch assemblage from the Oligocene–Miocene boundary of Ecuador". PeerJ. 8: e9051. doi:10.7717/peerj.9051. PMC 7195833. PMID 32391203.