The Rocky Mountains are the backbone of western North America, but on a map they are easy to misread. They are not the first mountains you meet driving east from the Pacific, they are not one continuous ridge, and several of the most famous ranges in the American West are not part of them at all.
Where the Rockies begin and end
The range runs from northern British Columbia in Canada, south through Alberta, Montana, Idaho, Wyoming, Utah and Colorado, and fades out in northern New Mexico. Between the Pacific coast and the Rockies sit other mountain systems, the Coast Mountains and Cascades in the north and the Sierra Nevada in California, and a wide band of plateaus and basins. The Rockies are the inland wall, rising directly out of the Great Plains on their eastern side.
The four sections
Maps usually divide the range into four parts, and each has its own character.
- The Canadian Rockies, along the border of Alberta and British Columbia, hold Banff, Jasper, Yoho and Kootenay national parks. They are steep, glaciated and dramatic, with icefields feeding rivers on both sides of the divide.
- The Northern Rockies, in Montana and Idaho, include Glacier National Park and long stretches of wilderness with few roads.
- The Middle Rockies, mostly in Wyoming, include the Tetons and the Yellowstone plateau, a volcanic highland rather than a typical mountain range.
- The Southern Rockies, in Colorado and northern New Mexico, are the highest section, with Colorado’s tallest summits and the Front Range rising behind Denver.
Between the middle and southern sections lies the Wyoming Basin, a broad gap of high plains that early railroads and today’s interstate use to cross the continent without climbing major passes.
The Continental Divide
The most important line on any map of the Rockies is invisible on the ground. The Continental Divide follows the crest of the range and decides which ocean a raindrop reaches. Water falling on the western side drains toward the Pacific, and water on the eastern side flows mostly toward the Atlantic, much of it by way of the Gulf of Mexico, while in Canada part of it heads for Hudson Bay and the Arctic.
You can see the idea in practice in Rocky Mountain National Park in Colorado. According to the National Park Service, Trail Ridge Road climbs to a high point of 12,183 feet, travels eleven miles above treeline, and crosses the Continental Divide at Milner Pass, at what the park calls a surprisingly low 10,758 feet. The high section of the road closes in winter, so check its status before planning a crossing outside summer.
The rivers that start here
Many of the great rivers of the American West and Midwest begin in the Rockies:
- The Columbia rises in the Canadian Rockies and flows to the Pacific.
- The Missouri begins in Montana and joins the Mississippi.
- The Colorado starts in Rocky Mountain National Park and runs south-west toward the Gulf of California.
- The Rio Grande rises in the San Juan Mountains of Colorado and forms much of the border between Texas and Mexico.
- The Arkansas and the Platte drain the eastern slopes onto the plains.
That is why so much of the water politics of the western United States comes back to snowfall in these mountains.
The national parks on the map
Much of the range is protected, and the parks make convenient landmarks when reading a map from north to south:
- Jasper and Banff in Alberta, linked by the Icefields Parkway.
- Glacier in Montana, across the border from Waterton Lakes in Canada.
- Yellowstone and Grand Teton in Wyoming, in the Middle Rockies.
- Rocky Mountain National Park in Colorado, on the Front Range.
- Great Sand Dunes in southern Colorado, where the Sangre de Cristo Mountains rise behind the dunefield.
What the Rockies are not
Three common map mistakes are worth correcting. The Sierra Nevada, with Yosemite and Mount Whitney, is a separate range in California. The Cascades, with Mount Rainier and Mount St Helens, are a volcanic chain closer to the coast. And the Colorado Plateau, with the Grand Canyon and the canyon country of Utah and Arizona, lies west of the Southern Rockies and is a raised table of rock rather than a mountain range.
Reading the Rockies in context
The range is one part of the larger continent shown on the map of North America, which places it between the plains and the Pacific mountain systems. For comparison across the Atlantic, the map of the Alps shows a range of similar fame that is far shorter but shared by many more countries. And for the highest mountains of all, the map of the Himalaya explains how a range built by a continental collision differs from the Rockies.
For current road conditions on the most famous crossing of the divide, the National Park Service keeps a Trail Ridge Road page with a recorded status line.
