During the Precambrian, around 1,200 million years ago, the ancient core of what is now eastern North America collided slowly with another continent to form a vast mountain range. All that remains today are the deeply eroded granites and gneisses of the Long Range mountains.
In the Precambrian, the supercontinent began to break apart. As it split, steep fractures formed and filled with molten rock from below. This magma cooled into the diabasedykes seen in the cliffs of Western Brook Pond and Ten Mile Pond.
By 570 million years ago the continent finally rifted apart, and the resulting basin became an ocean called the Iapetus Ocean. Some of the rocks of Gros Morne National Park were part of the continental margin on the western side of this new ocean, south of the Equator.