The paleomagnetic study of ash-flow tuff units aids in stratigraphic correlation of rocks of southwestern Utah. The Needles Range Formation is subdivided on the basis of three informal magnetostratigraphic episodes, the Cottonwood Wash normal, Wah Wah Springs reversed, and Minersville normal episodes, following the recommendations of the I.U.G.S. Subcommission (1973). The magnetic data support the conclusions of Anderson and Rowley (1975) as to the complexity of the Needles Range Formation; there appear to be two widespread units (Mackin, 1960) and many additional local units. It is impossible here to differentiate between the Blue Meadows Tuff and Baldhills Tuff Members of the Isom Formation. The spread of paleomagnetic data from the Baldhills Tuff Member may reflect the presence of numerous cooling units. Results from other formations are more negative because of the high frequency of magnetic field reversals. Differences in magnetic sign may rule out a proposed correlation, but similarity in magnetic sign supports, but cannot prove, a proposed correlation. The best representation of the original direction of magnetization in thick vertical sections in the Table Butte, Bauers, and Harmony Hills ash-flow tuff units comes from the central part of the units. This result complements the findings of Chevallier (1925) in his study of the lava flows of Mount Etna.