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The Catalina Island quartz diorite pluton yields a K-Ar date of 19 m.y. (middle or early Miocene) and amphibolite of the Catalina Schist 106 m.y. (Late Cretaceous). The first date gives an upper limit to the age of the overlying middle Miocene San Onofre (?) Breccia. Although the second date is somewhat younger than previously reported ages for similar Franciscan eclogites and amphibolites, it lends support to the correlation of the Catalina Schist with the Franciscan rocks in northern California. The Miocene pluton is of considerable interest because it is the only known “granitic” intrusion into the Franciscan rocks and because of its similarity to other West Coast plutons which intrude continental crust.

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