The lower two members of the Kunga Group, consisting of the Upper Triassic Sadler and Peril formations, represent the main limestone resource of the Queen Charlotte Islands, particularly the basal massive grey limestone comprising the 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, rests conformably on the Karmutsen Formation, and may be overlain conformably by the Jurassic Maude Group or disconformably by the Middle Jurassic Yakoun Group.

Light grey high-calcium limestone of the Sadler Formation outcrops on the southeast tip of Sandilands Island, in Skidegate Channel, just south of Maude Island. The beds strike west-southwest and dip 10 to 30 degrees northwest. The unit is bounded on the north by a northeast trending fault. The limestone is cut by irregular calcite veinlets up to five centimetres thick. The occasional grain of plagioclase is visible in thin section.