The Alsea Formation is a geologic formation in Oregon. It preserves fossils dating back to the Rupelian stage of the Oligocene period.

The following fossils have been reported from the formation:

• Aetiocetus cotylalveus
• Maiabalaena nesbittae
• Simocetus rayi

• Orthechinorhinus davidae

• List of fossiliferous stratigraphic units in Oregon
• Paleontology in Oregon

• Peredo, C. M.; Pyenson, N. D.; Marshall, C. D.; Uhen, M. D. (2018), "Tooth loss precedes the origin of baleen in whales", Current Biology, 28 (24): 1–9, Bibcode:2018CBio...28E3992P, doi:10.1016/j.cub.2018.10.047, PMID 30503622
• Welton, B. J (2016), "First report of Orthechinorhinus (Squaliformes: Etmopteriidae) from the Pacific Basin; A new species from Early Oligocene rocks of Oregon, USA", Fossil Record, 5: 303–308
• Deméré, T. A.; Berta, A. (2008), "Skull anatomy of the Oligocene toothed mysticete Aetiocetus weltoni (Mammalia; Cetacea): implications for mysticete evolution and functional anatomy", Zoological Journal of the Linnean Society, 154 (2): 308–352, doi:10.1111/j.1096-3642.2008.00414.x
• Fordyce, R. E (2002), "Simocetus rayi (Odontoceti, Simocetidae, new family); a bizarre new archaic Oligocene dolphin from the eastern North Pacific", Smithsonian Contributions to Paleobiology, 93: 185–222, doi:10.5479/si.00810266.93.185