In Arizona two major areas of deposition separated by Mazatzal Land had already been established by late pre-Cambrian time. The first Paleozoic transgression from the northwest, starting possibly late in the Early Cambrian and depositing the Tapeats sandstone, reached central Arizona. The southern limit of the Bright Angel shale and the overlap of the Muav limestone on the Tapeats indicate subsequent movements northward and southward in early Middle Cambrian time before the final withdrawal of the Cambrian sea from northern Arizona. In southeastern Arizona, likewise, only the earliest phase of the Cambrian transgression reached the central part of Mazatzal Land; the northwestern boundaries of the late Middle Cambrian Troy, Santa Catalina, Cochise, and the Upper Cambrian Abrigo formation are all successively regressive southeastward. Ordovician strata are known in Arizona only in the areas near New Mexico. Silurian and early Devonian deposits are present only near the extreme peripheral margins of Mazatzal Land beyond the limits of the State. Central-western Arizona was a positive element during the Ordovician, Silurian, and both the Early and Middle Devonian. The overlapping late Devonian transgression, also initiated from the northwest and southeast, deposited clastics around the central part of Mazatzal Land and was succeeded by deeper sea conditions in Mississippian time. The southeastern trough was the deeper of the two basins throughout the Late Paleozoic and is regarded as an arm of the Ouachita seaway. Following the retreat of seas from most of Arizona in the Late Mississippian a marked early Pennsylvanian transgression was introduced from the southeast and limited on the northwest by Mazatzal Land. Grading of the Manzano gypsiferous series and fossiliferous limestones into the Supai northward and distribution of Kaibab faunas establish the relation of the southeastern trough to the northern area of Permian shallow marine and continental deposition.