The region under consideration (Figure 1) lies within the Cabullona Basin of northeast Sonora. It is located south of the towns of Agua Prieta and Naco. The region covers an area of approximately 1850 square kilometers. The Agua Prieta region lies within the Basin and Range Province of northeast Sonora. The rocks exposed in the area are predominantly sedimentary rocks, although volcanic, plutonic, and metamorphic rocks are locally abundant (Figure 2). The Agua Prieta Area plays an important role in the paleotectonic interpretation of SE Arizona and NE Sonora. In general, the structural evolution of the region is poorly known and controversial. Pioneer field studies in the Agua Prieta region by Taliaferro (1933), Imlay (1939), and King (1934); as well as in adjacent areas by Ransome (1904) and Willson (1934) demonstrated that this region displays several structural and stratigraphic features that deserve more investigation. Recent studies by Rangin (1977) into late Cretaceous - early Tertiary tectonics of the Northern part of Sonora (Figure 2) suggested superimposed deformations and southwest directed thrusting in the Cabullona Basin. Paleontologic studies by Gamper and Longoria (1980) have shown that the Lower Cretaceous rocks of NE Sonora are predominantly open marine deposits, locally rich in planktonic foraminifera. Nevertheless, much remains to be learned about the tectonic evolution of the whole area.