Abstract

The Needles Range Formation is one of the most extensive of the middle Tertiary ash-flow sheets in the Great Basin of Nevada and western Utah. The original definition of the formation by Mackin (1960) named two members and mentioned three type localities. Our recent studies have shown that this published information now requires revision. To provide a firm basis for stratigraphic studies of the Needles Range Formation, this paper presents geologic maps, measured sections, and paleomagnetic data for three type localities in southwestern Utah. These include the northern Needles Range and Wah Wah Springs localities previously mentioned by Mackin, plus a new locality, northwest of Lund, Utah. The sequence of members at these localities, from oldest to youngest, is: Cottonwood Wash Tuff (new name), Wah Wah Springs Turf, Lund Tuff (new name), and Wallaces Peak Tuff (new name). We recommend abandonment of the name “Minersville Tuff.”

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