The Narcosli showing occurs within an area underlain by Tertiary sedimentary and volcanic rocks resting on older deformed rocks of the Cache Creek Group. The sedimentary rocks consist of sandstone, shale and conglomerate with interbedded tuff horizons, probably of Oligocene age, overlain by Miocene basalt flows. Outcrop is limited away from the incision of the Fraser River due to a cover of Pleistocene till.

The Narcosli showing is a surficial clay deposit, light brown in colour and with cone 2.5, suitable for common brick and tile manu- facture.