The objective of this study has been to determine areas potentially favorable for oil and gas exploration in southeastern Arizona. Surface geological investigations in the mountain ranges indicate that a thick sequence of marine sedimentary Paleozoic and Mesozoic (Cretaceous) rocks was deposited in the Pedregosa basin in southeastern Cochise County and adjacent shelf areas. According to Wengerd (1962), Kottlowski (1971), Greenwood (1969), and Greenwood and Kottlowski {1974), these marine strata deposited in this basin are similar in many aspects to those in petroleum-productive areas in southeast New Mexico and west Texas. They contain organic-rich basin facies of rocks that were probable sources for oil and gas. The margins of the Pedregosa basin offer structural, stratigraphic, unconformity, and paleogeomorphic traps. However, such adverse factors as the wide thickness variance of Cenozoic valley fill (100 feet or less to almost 12,000 feet), very little information as to the absence or presence of potentially petroleum-productive undeformed Paleozoic and Mesozoic rocks beneath Cenozoic rocks in the valleys, and extensive evidence in the mountains that the area has had an extremely complex geologic history, have discouraged exploration in the past.