Originally, all the rock of the Canadian Rockies lay flat on the shallow sea bed of the western continental shelf, where it had accumulated grain-by grain for over a billion years. About 175 million years ago, the continent of North America began to move westward, overriding the Pacific floor and colliding with offshore chains of islands.
The continental shelf was caught in the squeeze. The flat-lying layers slowly buckled into folds like those you see here. As time passed, folded mountain ranges sprang up across British Columbia. By 120 million years age, the Rockies were showing above the sea. They grew for another 75 millions years, rising faster than erosion could tear them down – likely reaching Himalayan heights. Active mountain building ended in the Canadian rockies 45 million years ago. The peaks have eroded to a small fraction of their original size.
