Most of the region is underlain by the Paleozoic to Tertiary Coast Plutonic Complex consisting predominantly of crystalline rocks which exhibit a variety of fabrics ranging from pre-to post- kinematic. Paragneisses of (?)Paleozoic age, younger deformed metasediments and volcanics related to the Stikinia Terrane are interspersed within the plutonic complex. The northeastern part of the Bella Coola map area is underlain primarily by mafic volcanic and sedimentary rocks of the Jurassic Hazelton Group. These rocks are variably deformed containing both northeast and northwest trending structures.
Between the Hazelton Group of the Stikinia Terrane to the east and the Coast Plutonic Complex with its deformed metasedimentary terrane to the west, is a belt of dominantly mafic rocks. These rocks are probably of volcanic origin and may be part of the Hazelton Group.
The Promise Well showing occurs entirely within a granodiorite batholith of the Coast Plutonic Complex. Mineralization occurs in a 21 metre wide band of garnet epidote skarn, consisting of magnetite with minor chalcopyrite. A pegmatitic stockwork cuts this skarn, another nearby skarn, and the granodiorite host rock. This pegmatite is anomalously radioactive with up to 0.006 per cent uranium oxide (Annual Report 1953 p. A166). The uraniferous mineral has not been identified.