Santa Cruz Mountain pluton
Santa Cruz Mountain pluton
Late Jurassic, ~147 Ma
A single mass intruding the Gopher Ridge Volcanics (unit CWGR), part of the Western Belt subterrane of the Cosumnes terrane north of Highway 140. Hornblende tonalite with subordinate biotite granodiorite in the eastern part of the pluton. Weakly deformed on the northeast, strongly mylonitic throughout most of the pluton. Saleeby and others (1989a) report a zircon U-Pb age of ~147 Ma for this pluton, along with a hornblende Ar-Ar age of ~146 Ma and a biotite Ar-Ar age of 141 Ma.