The area is underlain primarily by basalt and andesitic breccias. The Fort George Canyon placer deposit occurs on benches of the Fraser River.

"Data from the Cariboo mining district indicate that supergene leaching of gold dispersed within massive sulphides by Tertiary deep weathering followed by Cenozoic erosion is the most likely explanation for the occurrence of coarse gold nuggets in Quaternary sediments" (Exploration in British Columbia 1989, page 147).