The boundary separating the United States and Canada is the longest international border in the world, stretching approximately 8,891 kilometers. This immense length traverses a wide variety of terrain, meaning the two countries share much more than just a political line. While many geographical elements are shared, two massive systems stand out for their size and profound impact on the continent’s structure and history. These features are the continuous mountain chain along the west coast and the dominant freshwater network in the east.
The Shared Western Cordillera
The most dramatic shared physical feature is the Western Cordillera, a vast system of mountain ranges, plateaus, and basins that forms the geological backbone of western North America. This colossal belt of mountains extends from Alaska, through western Canada and the United States, and continues into Mexico. Its formation began between 170 million and 40 million years ago, as tectonic plates converged with the North American continent, pushing the land upward.
The Cordillera encompasses more than just the famous Rocky Mountains, which form its eastern spine. It also includes the Coast Mountains, the Cascade Range, and the Sierra Nevada, all running roughly parallel in a north-south direction. This shared geological history creates a continuous landscape characterized by sharp peaks, deep valleys, and significant mineral deposits in both countries.
The immense elevation of this shared range has a powerful effect on weather patterns across the continent. Moist air masses moving eastward from the Pacific Ocean are forced upward by the mountains, causing the air to cool and release precipitation on the western slopes.
This process, known as orographic lift, results in high rainfall and snowpack for the Pacific-facing slopes, while creating a distinct rain shadow effect over the interior plains to the east. The range also fosters a high level of biodiversity, supporting a wide array of plant and animal species that move freely across the international boundary.
The Great Lakes and St. Lawrence River System
Another defining feature shared by the two nations is the Great Lakes and St. Lawrence River System, the largest surface freshwater system on Earth. This network contains approximately 20 percent of the world’s fresh surface water. Four of the five Great Lakes—Superior, Huron, Erie, and Ontario—form a significant portion of the international boundary.
This system is connected to the Atlantic Ocean via the St. Lawrence River, which is made navigable by the St. Lawrence Seaway. This waterway enables ocean-going vessels to penetrate deep into the continent, reaching as far as Duluth, Minnesota. It supports a massive industrial and agricultural transportation hub for both countries, generating billions of dollars in economic activity.
The shared nature of this resource necessitates joint management, overseen by binational bodies like the International Joint Commission. Both countries rely on the lakes for drinking water, with a vast majority of Ontario’s population and many U.S. states drawing their supply from the basin.
The shared watershed is also diverse, home to thousands of species of plants, wildlife, and fish, requiring cooperative conservation efforts to protect the water quality and ecosystem.
The Vast Interior Plains
The expansive Interior Plains stretch from the Gulf Coast north to the Arctic Ocean. This region of low-lying, relatively flat terrain is situated between the Western Cordillera to the west and the Canadian Shield to the east. In the United States, this area includes the Great Plains, and in Canada, it is known as the Prairies.
The underlying geology is characterized by sedimentary bedrock, sculpted by past glaciation, resulting in rolling hills and low valleys. This shared topography and climate, which is susceptible to droughts, has led to a similar economic focus on both sides of the border. The soil in the central plains is rich and dark, formed by the accumulation of organic matter from grassland growth.
This continuous expanse is a massive agricultural zone, with the Canadian Prairies forming a northern extension of the U.S. Great Plains. Together, the two regions produce a significant portion of the world’s wheat exports and sustain North America’s beef cattle. Ecological zones, such as the mixed-grass prairie, transition seamlessly across the international line, tying the two nations together through a common agricultural landscape.