At the Clayoquot Arm North occurrence, three masses of limestone of the Upper Triassic Vancouver Group, Quatsino Formation, varying in size from 1250 by 500 metres to 2500 by 2000 metres, outcrop along several mountain tops 8 kilometres northwest of the head of Clayoquot Arm, 45 kilometres west of Port Alberni. The largest limestone mass is in fault contact to the north with volcanics of the Upper Triassic Vancouver Group, Karmutsen Formation and is partially overlain by Lower Jurassic Bonanza Group volcanics. All three masses are underlain by basalts and andesites of the Karmutsen Formation.