The Mo Group is underlain by a thick succession of highly deformed siltstones, greywackes and argillites of the Salmon River Formation, Bowser assemblage, and an Eocene augite diorite stock referred to as the Glacier Creek pluton (Grove 1971). The siltstones are folded and sheared, particularly around the margins of the intrusive. The northeast corner of Mo 2 extends over part of the Bitter Creek quartz monzonite intrusive. All rocks in the area are cut by a variety of dykes ranging from Portland Canal quartz monzonite and granodiorite, to Premier granodiorite porphyry and lamprophyres. Vein mineralization on the Mo Group is primarily confined to fracture systems within the Salmon River siltstones, although some mineralized veins have been found within the augite diorite stock.