The northern part of the Panamint Range, Inyo County, California, contains many early and middle Paleozoic marine formations, but precise stratigraphic relations are poorly known for lack of abundant megafossils and because of postdepositional dolomitization and silicification of the rocks.

The type section of the Hidden Valley Dolomite consists of 1,365 ft of light- to dark-gray, chert-bearing dolomite. On the basis of megafossil evidence, previous workers considered that the major part was Silurian and the upper 65 ft was Early Devonian.

Approximately 1,000 conodonts were identified from samples collected in a measured section about 1.5 mi north of the type section. Specimens from the uppermost 50 ft of the underlying Ely Springs Dolomite indicate a Late Ordovician or Early Silurian age. Conodonts from the Hidden Valley Dolomite indicate the presence of the European and eastern North America Neospathogathodus celloni zone and the younger Pterospathodus amorphognathoides zone within the lower 325 ft of the formation. Both zones are of Llandovery age (C₂-C₆) and represent the first report of Early Silurian conodont zones from the Death Valley area. The middle part of the formation yielded no conodonts, but a sparse fauna about 150 ft below the upper boundary contains specimens Polygnathus lingulifo mis and Icriodus latericrescens, suggesting an Early Devonian age. No diagnostic Devonian conodonts were recovered from the lower 100 ft of the overlying Lost Burro Formation.

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