Along the main line of the Canadian Pacific Railway between Hope and Yale, there are many outcrops of a light coloured, highly feldspathic rock. The iron content of the rock is low. A typical locality is reported to be exposed in the bed of American Creek, about 5 kilometres north of Hope. This occurrence is reportedly a pegmatite (Open File 1991-10, page 81).

The country rock underlying the area has been mapped as Custer Gneiss, a metamorphic assemblage probably derived from lower Mesozoic and possibly Paleozoic and Precambrian rocks, and metamorphosed in Late Cretaceous and early Tertiary time (GSC Map 41-1989). In this area, Eocene granodiorite intrudes the package.