The area is underlain by Lower Jurassic Bonanza Group volcanic rocks comprised mainly of andesitic to rhyodacitic flows, tuffs and breccia. Locally, the Bonanza Group rocks are intruded by granodiorite of the Jurassic Island Plutonic Suite.
Skarn-type copper, lead and zinc mineralization occurs along the contacts of granitic to rhyodacite dykes (related to the Island Plutonic Suite) where they intrude the Bonanza volcanics. Mineralization is comprised mainly of disseminated chalcopyrite with minor galena and sphalerite.