The Arcturus Formation was redefined by Wilson and Langenheim (1962) as a unit above the Riepetown and below the Kaibab Formations. Bissell (1964) raised the Arcturus to Group status and included within it the Riepe Spring Limestone, Riepetown Sandstone, Pequop Formation, and Loray Formation. This designation has been followed by later workers including Collinson (1968) and Stevens (1977). The units of the Arcturus Group are described separately. The Arcturus Formation is described separately as well to help the reader when sorting out older thesis and quadrangle mapping, as well as the published literature.