The transition from distributed continental extension to the rupture of continental lithosphere is imaged in the northern Gulf of California across the obliquely conjugate Tiburón‐Upper Delfin basin segment. Structural mapping on a 5–20 km grid of seismic reflection lines of Petroleos Mexicanos demonstrates that ~1000% extension is accommodated on a series of NNE striking listric‐normal faults that merge at depth into a detachment fault. The detachment juxtaposes a late‐Neogene marine sequence over thinned continental crust and contains an intrabasinal divide due to footwall uplift. Two northwest striking, dextral‐oblique faults bound both ends of the detachment and shear the continental crust parallel to the tectonic transport. A regional unconformity in the upper 0.5 s (two‐way travel time) and crest erosion of rollover anticlines above the detachment indicates inversion and footwall uplift during the lithospheric rupture in the Upper Delfin and Lower Delfin basins. The maximum length of new crust in both Delfin basins is less than 40 km based on the lack of an acoustic basement and the absence of a lower sedimentary sequence beneath a wedge‐shaped upper sequence that reaches >5 km in thickness. A fundamental difference exists between the Tiburón‐Delfin segment and the Guaymas segment to the south in terms of presence of low‐angle normal faults and amount of new oceanic lithosphere, which we attribute to thermal insulation, diffuse upper‐plate extension, and slip on low‐angle normal faults engendered by a thick sedimentary lid.

The Wagner basin occupies the northernmost spreading centre in the Gulf of California, located along the Pacific‐North America plate boundary. It is filled with sediments from the Colorado River that obscure its bathymetric expression; therefore it is not as well defined as other basins in the central and southern Gulf of California. To define the geometry and extension of the Wagner basin, a 2D multi‐channel seismic reflection database was used. Data were collected by Petroleos Mexicanos (PEMEX) in 1979–1980. The most important regional structural features identified are the Consag and Wagner normal faults and the Cerro Prieto strike‐slip fault. These structures play an important role in the development of the basin. The Consag fault, described for the first time in this paper, marks the western side of the basin. The eastern and northwest limits are bound by the Cerro Prieto and Wagner faults respectively. The Wagner fault intersects the Cerro Prieto fault at an angle of 130°, bending the depocentre in a NW direction, adjacent to the Cerro Prieto fault zone. The northernmost segment of the Consag fault bends 25° in a NE direction and joins the Cerro Prieto fault at an angle of 110°. Greater subsidence (up to 300 m) takes place along the northern trace of the Cerro Prieto fault, with a downthrown displacement of 400 m. The Consag and Wagner breaks obliquely intersect the Cerro Prieto fault, and, inasmuch as both are normal faults, they have small horizontal slip components which generated oblique displacement. This structural pattern is different relative to the pattern of basins located south of Wagner basin, such as the Upper and Lower Delfin basins. The orientations of the normal faults are perpendicular to the master fault (Ballenas transform fault). The relationship between normal and transform faults in the Wagner basin and the observed ‘S’ shape are typical of a basin that has not yet reached maturity. As a result of this study, the previously uncertain area (∼1330 km²) and perimeter (158 km) of the Wagner basin were defined.