The objective of this paper is to evaluate the eruptive setting of basaltic inclusions in the Sierra City melange, northern Sierra Nevada, California, through a detailed geochemical and petrographical study. The Sierra City melange is part of the pre-Upper Devonian Shoo Fly Complex which contains the oldest known oceanic rocks in the northern Sierra Nevada. The results show that the basalts are tholeiitic in composition and that they were probably erupted in a mid-ocean ridge, or marginal basin setting. These results suggest that the melange contains fragments of pre-Upper Devonian oceanic crust that must have existed along the western Cordilleran margin.
