Lake Combie complex
Lake Combie complex
Early Jurassic(?) to Late Triassic
Includes volcanic member of American River terrane of Graymer and Jones (1994). Mafic to intermediate plutonic and volcanic rocks and lesser ultramafic rocks at the structural base. Interpreted as an island arc volcanic assemblage overlying disrupted oceanic crust. Day and others (1985) correlated the Lake Combie complex with the Smartville Volcanic complex, but diorite from this complex near Colfax has yielded zircon U-Pb ages of ~203 Ma and ~198 Ma (Langenheim and others, 2025; Rack and Roeske, 2025). The volcanic member of the Lake Combie complex is interleaved with the Clipper Gap Formation (unit YACG) east of Auburn.