The western part of Canada falls into the territory of the province of British Columbia. This region is dominated by mountain ranges. The largest mountain ranges are the Canadian Rockies, Coast Mountains, Cassiar Mountains, and Columbia Mountains. All of these mountain ranges stretch roughly in a north-south direction.
The reason why this region is dominated by mountains is the geologic activity. The Pacific plate is subducting under the North American plate in this area. The subduction cause the land near the plate boundary to lift up, thus over time these mountains were formed. The process though is not over, as the subduction is still taking place and will for the foreseeable future, thus these mountain ranges should continue to grow and become even more dominant land features.