An enormous fan covering 202 to 243 hectares lies at the mouth of Joseph (Boulder) Creek where it empties into the North Thompson River, about 5 kilometres north of Little Fort. This is a collecting locality for boulders of jasper and red and green banded chert (Geological Survey of Canada Paper 72-53).

The area is probably underlain by Devonian to Permian Fennell Formation (Slide Mountain Group) pillow basalts, chert and argillite.