Mule Spring Limestone

The Mule Spring Limestone is a geologic formation in the Saline Range of eastern California and Split Mountain and Goldfield Hills of Nevada. It can also be found outcropping in the Inyo Mountains and White Mountains.

The formation also preserves fossils, primarily trilobites, dating back to the Cambrian period.

The Mule Spring Limestone, as its name suggests, is mainly composed of limestone rocks. These rocks are medium-gray to light-medium-gray, as well as very fine to fine crystalline, and is thin to very thin-bedded in most areas. In the lower sections of the formation, there are also occasional layers, up to 500 ft (150 m) thick, of pale-yellowish-brown or greenish-gray shale, limy siltstone and silty limestone.¹ In the Split Mountain, the formation overlies the Harkless Formation and underlies the Emigrant Formation,¹² whilst in other areas it overlies the Saline Valley Formation and underlies the Monola Formation.¹

The Mule Spring Limestone contains examples of Archaeocyatha, a clade of sponges that went extinct during this time,³ as well as a collection of trilobites.⁴¹

Genus	Species	Notes	Images
Bristolia1452	Bristolia sp. B. harringtoni B. insolens B. bristolensis B. anteros B. fragilis	Biceratopsid trilobites.
Peachella145	Peachella sp.	Biceratopsid trilobite.
Mesonacis4	Mesonacis sp.	Olenellid trilobite. Mesonacis sp. previously described as Fremontia sp. which was later synonymised into Mesonacis.1
Olenellus4562	Olenellus sp. O. puertoblancoensis(?)	Olenellid trilobite. Olenellus sp. previously described as Paedumias sp. which was later synonymised into Olenellus.1
Onchocephalus45	Onchocephalus sp.	Ptychoparid trilobite.
Ptychoparioid462	Ptychoparioid sp. A Ptychoparioid sp. B Ptychoparioid sp. C Ptychoparioid sp. D	Ptychoparid trilobites.
Bonnia1452	Bonnia sp.	Dorypygid trilobite.
Crassifimbra2	Crassifimbra sp.	Trilobite, family unknown.

Genus	Species	Notes	Images
Archaeocyathus3	Archaeocyathus sp.	Archaeocyathide sponge.