Rift-related magmatism in the northernmost Gulf of California and the adjacent subaerial Salton Trough and Cerro Prieto basins comprises intermediate to rhyolitic surfi cial and buried lava fl ows and domes, including their xenolith cargo. In addition, geothermal drill wells frequently penetrate subsurface gabbroic to granitic sills and dikes, which intruded into Colorado River delta fl uviatile and lacustrine sediments. Combined singlecrystal U-Th-Pb and (U-Th)/He zircon ages reveal late Pleistocene to Holocene eruption ages for three volcanic centers in adjacent rift basins (from N to S): Salton Buttes (eruption age: 2.48 ± 0.47 ka; 95% confi dence), Cerro Prieto (maximum eruption age: 73 ± 7 ka), and Roca Consag (eruption age: 43 ± 6 ka). U-Th zircon and allanite crystallization ages are close to the eruption ages, with the exception of Roca Consag lava, the zircon population of which is dominated by zircon with ca. 1 Ma crystallization ages, a population interpreted to be recycled from an unknown crustal source underlying the Wagner basin. Nd isotopic ratios for subsurface micro gabbros from Cerro Prieto (eNd = +8.9) overlap with values for midoceanic-ridge basalts (MORB) from the East Pacifi c Rise, adjacent to the southern Gulf of California. Cerro Prieto microgranites and Salton Sea basaltic xenoliths have similarly elevated eNd values. The lowest eNd value for late Pleistocene–Holo cene igneous rocks from the northern Gulf of California is for Cerro Prieto dacitic lava (eNd = +0.6). This value implies minor (<20%) assimilation of continental crustal rocks, which, however, is an upper limit because of crystal-scale evidence for magma contamination by unconsolidated sediment at the time of eruption. Zircon crystals in felsic rocks (rhyolite lavas, intrusive microgranites, and granophyre xenoliths) have trace-element and submantle δ 18 O compositions that are robust indicators for a mafi c source that has exchanged oxygen by interacting with meteoric hydrothermal fl uids. Collectively, these data imply that oceanic rifting has initiated in the Salton Trough and Cerro Prieto basins. There, MORB-type magmas formed mafi c intrusions within thick sedimentary basin fi ll, where they became exposed to deep-reaching hydrothermal fl uids. Diverse intermediate- to high-silica rhyolitic magmas that are prevalent at the surface are produced by fractional crystallization of mafi c parental magmas with minor assimilation of sediments or pre-rift basement rocks, and by partial melting of hydrothermally altered mafi c intrusions.