Mesozoic sandstones from six rock units that underlie the Jurassic-Cretaceous arc of peninsular California appear to contain a mixture of late Paleozoic-early Mesozoic zircons and a mixture of Precambrian zircons averaging about 1,540 Ma. These data suggest that the detrital zircons were derived from the southwestern United States and northern Mexico during late Triassic-early Jurassic time.

Two of six Paleozoic sandstones contain detrital zircons whose average U-Pb age is 1,500 Ma. This age is similar to the average age of Precambrian basement in adjacent Arizona and Sonora. However, three of the six Paleozoic sandstones contain zircons whose average U-Pb age is two billion years or greater. This age exceeds that of possible source rocks located in the southwestern Cordillera, but is similar to U-Pb ages for detrital zircon in the Shoo Fly Complex of the northern Sierra Nevada (Girty and Wardlaw, 1985; Miller and Saleeby, 1991).