Grass Valley pluton
Grass Valley pluton
Late Jurassic, ~159-162 Ma
Intrudes the Lake Combie complex beneath and south of the town of Grass Valley. Medium- to coarse-grained gray to pinkish-gray hornblende granodiorite, with biotite locally. This unit has a zircon U-Pb age of ~159 Ma (Irwin and Wooden, 2001), as well as amphibole Ar-Ar ages of ~160 and ~162 Ma, and a biotite Ar-Ar age of ~162 Ma (Taylor and others, 2015).