The names Ely (Early Pennsylvanian) and Park City (Medial Permian), which for years were known at the formation level, have recently been raised to group rank in parts of Nevada and Utah. The name Arcturus has been used by stratigraphers for rocks of Permian age in this same area, but considerable confusion attends its present concept; it is herein proposed to raise it to group rank to include, in ascending order, these formations: Riepe Spring Limestone (Early to Medial Wolfcampian age), Riepetown Formation (Medial to Late Wolfcampian age), Pequop Formation (Leonardian age), and Loray Formation (Late Leonardian-Early Wordian age). In northeastern Nevada and northwestern Utah the Ferguson Mountain Formation (mostly of Wolfcampian age) is present beneath the Pequop Formation and is equivalent (in part at least) to the Riepe Spring and Riepetown; it is not proposed to include it in the Arcturus Group. As now understood, the Ely, Arcturus, and Park City Groups include numerous rock types (mostly marine) including a large spectrum of limestones, siltstones, claystones, shales, dolomites, evaporites, sandstones, and orthoquartzites. Areal distribution includes much of east-central and northeastern Nevada and west-central lo northwestern Utah.

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