During the Middle Jurassic the Twin Creek Limestone was deposited in the Nevada Foreland Basin. Ammonites are found in the Sliderock Member of this Formation.
Reference: Imlay, R. W., 1967, Twin Creek Limestone (Jurassic) in the Western Interior of the United States, U.S.G.S. Professional Paper 540
Megasphaeroceras rotundum Imlay 1962,
this specimen is 47mm diameter
Eocephalites primus Imlay 1967, this
specimen is 90mm diameter
Stemmatoceras n. sp. aff.
albertense Mclearn 1928, this specimen is 210mm diameter
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