Tascotal Mesa fault is the principal component of Tascotal Mesa transfer zone within the Rio Grande rift of Texas (USA) and Chihuahua (Mexico). Strata and structures along the zone attest to ~290 m.y. of tectonic and magmatic activity, from at least late Paleozoic time onward. The transfer zone comprises the Tascotal Mesa and newly documented Christmas Mountains–Grapevine Hills faults, as well as the Terlingua Creek pull-apart complex at the right step between those two dextral zones. Strike-slip (to ~1 km) and dip-slip (to ~735 m) displacements have occurred in the zone during the past 30–27 m.y.; young faults of the transfer zone displace mid-Pleistocene caliches. Stable isotope and palynologic data from travertines in the transfer zone indicate ascent of warm waters (25°–35 °C) along faults as recently as mid- to late Pleistocene time. Older, basement-rooted structural anisotropies are present in the Tascotal Mesa transfer zone but not all have been reactivated during Cenozoic rifting. Geophysically constrained physical models integrated with field data demonstrate that the Terlingua Creek pull-apart basin likely formed in cover strata that were detached from basement, as the orientations of surficial and buried basement structures differ markedly. Dip-slip displacement predominates on pull-apart faults, with significant dextral slip. Analysis of the role of the Tascotal Mesa transfer zone in Rio Grande rifting revealed that it and the flanking grabens (Presidio to the northwest; Redford to the southeast) are all parts of the Border Corridor transform zone. This transform zone interconnects rift segments from Mesilla graben to the Sunken Block and includes both transfer zones and grabens. Right-transtensional deformation, as manifested in historic earthquakes, accounts for differing orientations of transform (northwest) versus rift (north) grabens. Petrographic and geochronologic data indicate ascent of lavas of rift geochemical character in both the Tascotal Mesa transfer zone and the Border Corridor transform zone from ca. 30 Ma onward. K-Ar ages were determined for basalt (24.73 ± 1.96 Ma) and trachyte (25.42 ± 0.64 Ma) emplaced within the Tascotal Mesa transfer zone. Magmatism is bimodal; olivine basalt and/or hawaiite predominates. Basalts at the junctions of rift grabens and the Border Corridor transform zone entrain mantle and lower-crustal xenoliths.

Of all the countries in the world considered to be oil rich, Mexico is the only one that consistently has been losing production and reserves in the last ten years. Even though Mexico has five major producing provinces: two for oil (the Southeast and the Tampico–Misantla basins) and three for gas (the Sabinas, Burgos and Veracruz basins), and has seven more with potential, (California, Gulf of Cortès, Chihuahua, Sierra Madre Oriental, Sierra de Chiapas, Progreso shelf, and the deep Gulf of Mèxico), its output and reserves have declined consistently. Many reasons can be attributed for these results, and as this note proves, least of them is the country’s endowment of oil and gas resources. The problem is that Mexico, since 1938, has had only one oil company responsible for all of its upstream activities and even though Pemex’s performance is comparable with that of most of the majors’ (it is world’s third largest in terms of production), it is impossible that all the remaining potential of the entire country can be found and produced with only one company, no matter how large, wealthy, efficient, technologically advanced, and successful it can be. The good news is that once the country opens up for third-party participation in exploration, which will eventually take place, results are going to be spectacular. So far there has only been a timid opening for development and exploitation opportunities.

The western pupfish clade (Cyprinodontidae: Cyprinodon) consists of nine species that occur primarily in isolation from one another in the large area extending from the Guzmán Basin, northwestern Chihuahua, Mexico, to the Death Valley region of southeastern California and southwestern Nevada. This paper presents a reassessment of estimated divergence times based on a compilation of previously published mitochondrial DNA sequences (ND2, cytb, and control region). The results agree with previous estimates, which state that the western pupfish clade originated in the late Miocene or early Pliocene and that Cyprinodon was present in the Death Valley region by at least the middle Pliocene and possibly earlier. Enigmatically, there is little geologic evidence of late Neogene surface-water connections among the Guzmán, Lower Colorado River, and Death Valley regions. This indicates that either our knowledge of such connections is incomplete or pupfish dispersal across basin divides via small, relatively transient, surface-water connections has been more common than expected based on the low-gradient, valley-floor habitats generally occupied by this group.