The lower two members of the Jurassic to Triassic Kunga Group, Sadler and Peril Formations, represent the main limestone resource of the Queen Charlotte Islands, particularly the basal massive grey limestone member (Sadler Formation). Its thickness varies from less than 30 metres to more than 200 metres.

The Kunga Group consisting of the limestone members and an overlying argillite member, Sandilands Formation, rests conformably on the Vancouver Group, Upper Triassic Karmutsen Formation.

The Sadler limestone strikes northwest across the centre of Kunghit Island.