The Hidden Creek area is underlain by Early and Middle Jurassic Ladner Group sediments east of the Hozameen fault, a major, steeply dipping, north-northwesterly trending fracture system which separates rocks of the Methow-Pasayten trough from members of the Permian to Jurassic Hozameen Complex to the west. Most of the mineral occurrences in the area lie east of but generally close to this fault, which encloses metaplutonic rocks of the Coquihalla serpentine belt between Mount Dewdney and Siwash Creek. The Ladner Group and, to a lesser extent, Hozameen Complex rocks are cut by a variety of small intrusive bodies ranging in composition from gabbro through granodiorite to syenite.

The Gold Coin occurrence is described as being situated near the western contact of a belt of rocks characterized by serpentinite. These rocks are in contact with black, carbonaceous slate and argillite. The sediments host quartz, occurring as irregularly distributed bunches and stringers, adjacent to the contact as well as oxidized pyrite and pyrrhotite.

The Gold Coin tunnel exposes iron-stained, altered argillite and serpentine which, near the portal, is particularly schistose and hosts "rotten" quartz, talc and platy slate fragments. A 1.52-metre wide sample taken from this area assayed 82.97 grams per tonne gold (Crossland, 1935 - Property File).