Correlation of Cambrian strata in the western part of the Grand Canyon involves consideration of formations and faunas from eastern and southeastern Nevada and from the Granite Gorge area of the Grand Canyon in Arizona. Lithologic units defined in both regions are recognized. With priority of definition as the basis for acceptance of formational names, all units to which such definitions apply have their type localities in the Basin Range region. The Cambrian sequence near Grand Wash Cliffs in the westernmost part of the Grand Canyon contains 179 feet of Lower Cambrian Prospect Mountain quartzite (Eureka district, Nevada), which rests unconformably upon pre-Cambrian granite gneiss. These rocks are overlain by 304 feet of Lower and Middle Cambrian Pioche shale (Pioche district, Nevada), carrying the Olenellus zone fauna at the base and Albertella near the top. Above the Pioche formation lie 70 feet of strata consisting of two massive dolomite members separated by 40 feet of sandstone, shale, and dolomite. This unit is the lithogenetic equivalent of the Lyndon limestone (Pioche district). The Lyndon is followed by 99 feet of Chisholm shale (Pioche) with the Glossopleura zone fauna. The Chisholm formation is in turn overlain by about 380-400 feet of Peasley limestone (Pioche). All the above-mentioned Cambrian formations are conformable in western Grand Canyon. The last three are of medial Cambrian age. Disconformably above the Peasley limestone lie 110 feet or less of limestones of probable medial Cambrian age. These beds, which here are named the "Mead formation," are disconformably overlain by a thick series of undifferentiated dolomites and limestones of Cambrian(?) and post-Cambrian Paleozoic age.