Zircons in volcanic rock clasts of the Eocene Poway Conglomerate in San Diego County, California, have lead-alpha dates that range from 190 to 260 m.y. Three similar felsites of the Sidewinder and Hodge Volcanic Series in the central Mojave Desert range from 210 to 260 m.y. in age. Because no other similar rocks of this age are known to exist in Southern California or adjacent areas, it is tentatively concluded that many felsite clasts of the Poway Conglomerate were originally derived from Permian-Triassic rocks of the Mojave Desert.

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