Big Red lies with the Stikine Terrane of the Intermontane Belt of the Canadian Cordillera between the Coast Belt and the Bowser Basin.  It comprises Paleozoic and Mesozoic arc volcano-sedimentary rocks and coeval plutonic complexes which are overlain by marine clastic rocks of the Bowser Lake Group which are in turn overlain by continental strata of the Sustut and Sloko.