AGE OF THE INTRUSIVE ROCKS OF THE SOUTHEASTERN SAN GABRIEL MOUNTAINS, CALIFORNIA
Dating of the intrusive rocks of the southeastern San Gabriel Mountains by the Rb-Sr and by the K-A methods indicates two periods of plutonic intrusion. A concordant quartz diorite pluton, dated as 83–105 m.y., was emplaced during the Cretaceous orogeny. Small discordant quartz monzonite plutons, dated as 17–26 m.y., were emplaced during the Miocene orogeny. These dates permit a correlation of the geologic history of the southeastern San Gabriel Mountains with that of the Los Angeles basin.