Which mountain range runs along the border between the United States and Canada?

The Rocky Mountains are the mountain range that runs along the border between the United States and Canada. This vast and prominent range extends over 3,000 miles from northern British Columbia in Canada, through the United States down to New Mexico. The Rockies mark a natural boundary across several states and provinces and are known for their stunning landscapes, diverse wildlife, and important ecosystems. They play a significant role in the geography of North America, influencing weather patterns and serving as a crucial watershed for many rivers.

In contrast, the Appalachian Mountains, while significant in the eastern United States, do not extend into Canada. The Sierra Nevada, located primarily in California, and the Coast Mountains, found in western Canada, are geographically distinct from the U.S.-Canada border. Hence, the Rocky Mountains are uniquely positioned as the correct answer to this question.