The Tanzilla Butte showing is centred on the southernmost limestone outcrop on Little Eagle River, about 16.5 kilometres east of the community of Dease Lake.

Various limestone beds of the Upper Triassic Sinwa Formation (Stuhini Group) outcrop discontinuously over a 6 by 19 kilometre area across the north slope of Tanzilla Butte. They generally trend west-northwest and dip moderately northeast. The limestone is commonly argillaceous and fetid.