The western half of Quadra Island is underlain primarily by andesitic volcanic rocks of the Upper Triassic Karmutsen Formation which are overlain and bounded on the east by a northwest trending belt of Upper Triassic Quatsino Formation limestone, both of the Vancouver Group.

The area is underlain by highly fractured and sheared Upper Triassic Karmutsen Formation amygdaloidal andesitic flow rocks interlayered with dense, fine to medium grained andesitic units and minor thin beds of sedimentary and tuffaceous material. The flow rocks dip gently south and southeast and range in thickness from 0.3 to 3.6 metres and more. Many of the flows are highly amygdaloidal with the amygdules filled with calcite, quartz, chlorite, actinolite or prehnite. The rocks are chloritized and cut by numerous stringers and veinlets of quartz, calcite and epidote.

At the Inca occurrence a well defined quartz vein 0.6 to 1.8 metres in width cuts the andesite and is mineralized with pyrite and chalcopyrite. A portion of the vein on one wall is rose quartz.

The quartz vein has been explored by an open cut and shallow shaft.