Workers in Sonora recognize two distinct provinces of Upper Proterozoic and Paleozoic strata; one of shallow-water origin and one of deeper-water origin. The shallow-water miogeoclinal strata are best known in areas west and southwest of Caborca, and range in age from late Proterozoic to Permian. These correlate with strata in the Sierra Agua Verde-Cerro Cobachi area east of Hermosillo. Strong stratigraphic similarities between these rocks and those of Nevada have fueled hypotheses that they were adjacent in Paleozoic time and have been separated 800 km by left-lateral strike-slip displacement of mid-Jurassic age. Deeper-water strata occur farther to the south and southeast in Sonora where rocks of Ordovician to Permian age contain bedded cherts and carbonate turbidites. These rocks in the Sierra Cobachi and at Barita de Sonora resemble similar-age slope- and basinal-facies rocks in Nevada, and in like fashion appear to be thrust northward or eastward over the miogeoclinal facies. Both of these fades also occur in the basement strata of peninsular California. Carbonate rock, quartzite, amphibolite, and subordinate argillaceous strata crop out from the San Jacinto Mountains of southern California to the southeastern Sierra San Pedro Martir (Baja California Norte). The only age control on these rocks are the Early Ordovician conodonts found on Coyote Mountain, Imperial County, California. Deep-water strata with pillow basalt and a cratonal sedimentary contribution are found in the Sierra las Pinta and along the Gulf Coast of Baja California between Puerto Calamujue and Bahia Los Angeles. Ages based on poorly preserved conodonts and corals range from Devonian to Mississippian, but the rocks may not be limited to this age span. Similar strata, dominated by bedded chert, occur on Isla Angel de la Guarda, at the southeastern tip of Isla Tiburón and on the adjacent coast of Sonora, thus effectively connecting across the Gulf of California. Analogous deep-water-facies strata, dominated by bedded chert, occur in northern Sinaloa. Conodonts from San José de Gracia, Sinaloa, indicate a Pennsylvanian age. If the apparent correlations of both miogeoclinal and deeper-water facies of Paleozoic strata across the Gulf of California are correct, they put constraints on the paleomagnetic reconstructions that place peninsular California in southern Mexico in Late Cretaceous time.