Santiago Formation, California

For other uses, see Santiago Formation.

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).^[1]

Santiago Formation
Stratigraphic range: Late Eocene-Late Oligocene (Uintan-Duchesnean)
Type	Geological formation
Lithology
Primary	Siltstone, mudstone
Other	Sandstone
Location
Coordinates	33.1°N 117.3°W / 33.1; -117.3
Approximate paleocoordinates	33.3°N 104.1°W / 33.3; -104.1
Region	Orange & NW San Diego County, California
Country	United States
Santiago Formation, California (the United States) Show map of the United States Santiago Formation, California (California) Show map of California

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 25 °C (77 °F).^[2]

Fossil content

Mammals

Ferae

Ferae reported from the Santiago Formation
Genus	Species	Presence	Material	Notes	Images
Ceruttia	C. sandiegoensis	Member C.[3]	Jaw elements & teeth.[3]	A carnivoraform also found in the Mission Valley Formation.
Diegoaelurus	D. vanvalkenburghae	"Member C".[4]	A nearly complete dentary.[4]	An oxyaenid.
Lycophocyon	L. hutchisoni	Upper portions of "member C".[5]	Multiple specimens.[5]	A basal caniform.
Procynodictis	P. progressus	Member C.[3]	Jaw elements & teeth.[3]	A miacid also known from the Sespe & Mission Valley formations.

Primatomorphs

Primatomorphs reported from the Santiago Formation
Genus	Species	Presence	Material	Notes	Images
Chumashius	C. balchi	V-72088.[6]	Isolated teeth.[6]	An omomyid also known from the Sespe Formation.
Dyseolemur	D. pacificus	V-72088.[6]	Isolated molars.[6]	An omomyid also known from the Sespe Formation.
Walshina	W. esmaraldensis	Member C.[7]	Teeth.[7]	An omomyid also known from the Mission Valley & Sespe formations.

Ungulates

Ungulates reported from the Santiago Formation
Genus	Species	Presence	Material	Notes	Images
Hesperaletes	H. borineyi	Member C.[8]	Numerous specimens.[8]	A tapiroid.
Parvicornus	P. occidentalis	Member C.[9]	Numerous specimens.[9]	A brontothere.
Protoreodon	P. walshi	Member C.[10]	Numerous specimens.[10]	An oreodont.
	P. cf. walshi	Member C.[10]	Jaw elements.[10]	An oreodont.

Invertebrates

Invertebrates reported from the Santiago Formation
Genus	Species	Presence	Material	Notes	Images
Upogebia	U. aronae	Member B.[11]	Numerous specimens.[11]	A mud shrimp.

See also

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