In the Rio Grande rift of southern New Mexico, the intrabasinal East Robledo fault in the Mesilla basin and the Jornada fault in the Jornada del Muerto basin experienced hundreds of meters to kilometers of offset during late Miocene to early Pliocene time and tens of meters of offset since middle Pleistocene. Late Pliocene and early Pleistocene activity on the faults is assessed by comparing sedimentological characteristics of the Camp Rice Formation, which is correlated by reversal magnetostratigraphy, on either side of the faults. The Jornada fault is interpreted to have been inactive from approximately 3.4 to 2.5 Ma, because Gauss-age fluvial strata at Rincon Arroyo, located on the hanging wall, have similar sediment accumulation rates, degree of development of calcic paleosols, and relative abundance of fluvial channel lithofacies as coeval footwall strata at Cedar Hill and Lucero Arroyo. In contrast, syndepositional movement on the Jornada fault along the northern flank of the Dona Ana Mountains from 2.5 to 0.7 Ma is suggested by a condensed Matuyama interval characterized by mature stage III and IV calcic paleosols at Lucero Arroyo. The northern segment of the East Robledo fault was active during Gauss time, based on an abundance of relatively thick (59 m), fluvial-channel deposits in the hanging-wall section at Northeast Robledo. The southern segment of the East Robledo fault, however, was probably not active during most of Gauss time, because of the presence on the footwall of a thick (50 m) section of fluvial strata of Gauss age at Picacho Mountain. Major movement on the East Robledo fault near the end of Gauss time terminated sedimentation at Picacho Mountain and in the Corralitos basin, abandoning the upper La Mesa geomorphic surface.

Abstract Possible future petroleum provinces in southwestern New Mexico and southern Arizona are: (1) Tularosa Valley and Jornada del Muerto basins, where they include parts of the late Paleozoic Orogrande basin in western Otero, eastern Dona Ana, and eastern Sierra Counties; (2) Paleozoic Pedregosa basin of southern Hidalgo and southeastern Cochise Counties (and adjacent parts of Chihuahua in Mexico); (3) Estancia basin in central Torrance County; (4) south flanks of the Zuni Mountains in Valencia, northwestern Socorro, and northern Catron Counties; and (5) small buried Pennsylvanian basins, such as the Lucero basin in eastern Valencia and northwestern Socorro Counties and the San Mateo basin in southwestern Socorro County. Paleozoic beds with petroleum potential that were deposited in the Pedregosa basin area in southeast Arizona and southwest New Mexico consisted of more than 4,800 cu mi (20,000 cu km); the original Paleozoic section in the Orogrande basin consisted of about 7,200 cu mi (30,000 cu km) of marine carbonate rocks and sandstone-shale beds. Shoreline and nearshore sandstone lenses, algal reef mounds, and shelf-edge bioclastic carbonate banks of Pennsylvanian and Early Permian age, associated with nearby black, organic-rich basinal facies, are primary petroleum targets of the late Paleozoic basin areas, such as the Pedregosa and Orogrande basins, which are similar to the petroliferous Permian basin. Porous dolomite in Leonardian and younger Permian carbonate rocks offers porosity traps in sequences rich in organic materials. The thick Lower Cretaceous sequence in the Pedregosa region contains sandstone wedges, coralline reefs, and bioclastic banks which all are possible reservoirs. Ordovician and Silurian dolomite beds, especially where overlain by truncating black, shaly Devonian strata, are possible stratigraphic-trap reservoirs, as are the locally porous, biohermal, "crinoidal-hash" limestone beds of the Mississippian.