Abundant and diverse conodonts indicate age revisions or refinements for Upper Ordovician, Silurian, and Lower Devonian rocks in the southwestern Great Basin. Measured sections from the Inyo Mountains, northern Panamint Range, and Nopah Range in California and from the Bullfrog Hills in Nevada include the Ely Springs Dolomite, Roberts Mountains Formation, Hidden Valley Dolomite, Vaughn Gulch Limestone, and Sunday Canyon Formation. Using conodonts as indicators, ages of these formations are as follows: (1) the Ely Springs Dolomite ranges from latest Middle Ordovician to Early Silurian, (2) the Roberts Mountains Formation ranges from Early to Late Silurian, (3) the Hidden Valley Dolomite ranges from Early Silurian to Early Devonian, (4) the Vaughn Gulch Limestone ranges from Early (?) Silurian to Early Devonian, and (5) the Sunday Canyon Formation ranges from Early to Middle(?) Devonian.