The area is underlain by Upper Triassic Karmutsen Formation vol- canic rocks of the Vancouver Group. These are interbedded with, and overlain to the northeast by a northwest trending belt of Quatsino Formation limestone (Vancouver Group) known historically as the "lime-belt". The Vancouver Group rocks are in fault and/or intrusive contact to the northeast with intrusive rocks of the Juro-Cretaceous Coast Plutonic Complex.
The Sea Gull showing consists of an irregular mass of quartz "several feet" in width developed along the contact between granitic intrusive rock and limestone. The quartz contains some disseminated pyrrhotite and chalcopyrite as well as occasional flakes of molyb- denite (Geological Survey of Canada Summary Report 1913).