The Santiago Formation is a geologic formation in Orange and northwestern San Diego County, California. The siltstones, mudstones and sandstones of the formation preserve fossils of Walshina esmaraldensis and Diegoaelurus vanvalkenburghae, dating back to the Late Eocene to Late Oligocene periods (Uintan to Duchesnean in the NALMA classification).Kelly Ranch Core at Fossilworks.org
Depositional environment The only paleoenvironmental interpretation based exclusively on specimens from the Santiago Formation is a study of land snails from SDSNH locality 3276 (Member C, Oceanside, San Diego County), which found the distribution of shell sizes and shapes to be consistent with interpretations of subtropical to tropical conditions and paleotemperatures in excess of .López Torres et al., 2018, p.5
Fossil content Mammals Ferae Ferae reported from the Santiago Formation Genus Species Presence Material Notes ImagesCeruttiaC. sandiegoensisMember C.Jaw elements & teeth.A carnivoraform also found in the Mission Valley Formation.DiegoaelurusD. vanvalkenburghae"Member C".A nearly complete dentary.An oxyaenid.LycophocyonL. hutchisoniUpper portions of "member C".Multiple specimens.A basal caniform.ProcynodictisP. progressusMember C.Jaw elements & teeth.A miacid also known from the Sespe & Mission Valley formations.
Primatomorphs Primatomorphs reported from the Santiago Formation Genus Species Presence Material Notes ImagesChumashiusC. balchiV-72088.Isolated teeth.An omomyid also known from the Sespe Formation.DyseolemurD. pacificusV-72088.Isolated molars.An omomyid also known from the Sespe Formation. WalshinaW. esmaraldensis Member C.Teeth. An omomyid also known from the Mission Valley & Sespe formations.
Ungulates Ungulates reported from the Santiago Formation Genus Species Presence Material Notes ImagesHesperaletesH. borineyiMember C.Numerous specimens.A tapiroid.ParvicornusP. occidentalisMember C.Numerous specimens.A brontothere.ProtoreodonP. walshiMember C.Numerous specimens.An oreodont.P. cf. walshiMember C.Jaw elements.An oreodont.
Invertebrates Invertebrates reported from the Santiago Formation Genus Species Presence Material Notes Images UpogebiaU. aronae Member B.Numerous specimens. A mud shrimp.
See also List of fossiliferous stratigraphic units in California Paleontology in California
References
Bibliography
Further reading Prothero, D.R. 2001. Magnetic stratigraphy of the middle-upper Eocene Santiago Formation, Orange and San Diego Counties, California. Guidebook, Pacific Section, Society of Economic Paleontologists and Mineralogists, 91:107-118