The Tanzilla Valley occurrence is centred on the surface trace of a limestone band on the southeast side of the Tanzilla River valley, about 41 kilometres southwest of the community of Dease Lake.

A unit of Lower Permian Stikine Assemblage pale grey and orange cherty limestone and argillaceous limestone trends northeastward along the southeast side of Tanzilla River valley. The underlying basalt, andesite, tuff, breccia and clastic sediments of the Upper Triassic Stuhini Group outcrop on the east side of the band.