The Table Mountain bentonite showing occurs within an assemblage of rhyolitic tuff of Eocene age west of the Fraser Fault, which are correlative with the Kamloops Group east of the fault. These volcanics comprise an overlap assemblage on the Methow Terrane of the Intermontane tectonic belt.

White bentonitic ash layers, recognised over an area of 100 metres by 750 metres, occur within a succession of pink to maroon andesitic to dacitic volcanic breccia.