The ridge traces its history to the Triassic period when this part of Nova Scotia occupied the center of the supercontinent Pangaea. It is a 201 million year old sequence of tholeiitic basalts, which contains columnar jointing. The basalts also extend under the Bay of Fundy and parts of it are exposed on the shore at Five Islands, east of Parrsboro on the north side of the bay. Numerous sediment-filled fissures are present near the upper surface of North Mountain. The hard ridge of basalt resisted the grinding of ice sheets that flowed over the region during past ice ages, and now forms one side of the Annapolis Valley in western part of the Nova Scotia peninsula.