Montana’s geography splits into two halves along the Continental Divide: the northern Rocky Mountains, with more than a hundred named ranges, fill the west, while the Great Plains cover about 60 percent of the state to the east, broken by isolated “island” ranges, river breaks and badlands. The highest point is Granite Peak in the Beartooth Mountains, 3,904 m (12,807 ft), and the lowest is the Kootenai River where it leaves for Idaho, about 549 m (1,800 ft). The main rivers are the Missouri, which begins at Three Forks; the Yellowstone, the longest undammed river in the lower 48 states; and the Clark Fork, the largest by volume. Flathead Lake, at 510 km² (197 sq mi), is the largest natural freshwater lake in the western United States. With 380,800 km² (147,040 sq mi), Montana is the fourth-largest state and the largest with no coastline.
Its rivers drain to three different seas. Water west of the divide reaches the Pacific through the Columbia; water east of it reaches the Gulf of Mexico through the Missouri and Mississippi; and a strip along the Canadian border in Glacier National Park sends its rivers north to Hudson Bay. This guide starts at the summit and follows the water down.
Granite Peak and the Beartooth Plateau: Above 3,000 Metres
Montana’s summit stands in the Absaroka-Beartooth Wilderness of Park County, 16 km (10 mi) north of the Wyoming border. Granite Peak is often called the second-hardest state high point to climb after Denali, because reaching it needs technical rock climbing, route-finding and luck with the weather. It was the last of the 50 state high points to be climbed: Elers Koch, James C. Whitham and R. T. Ferguson reached the top on 29 August 1923 after several earlier parties had failed. Climbers usually take two or three days, camping on the aptly named Froze-to-Death Plateau.
The Beartooth Mountains sit on a broad, high tableland, the Beartooth Plateau, just northeast of Yellowstone National Park. U.S. Highway 212, the Beartooth Highway, climbs from Red Lodge onto the plateau and crests just over the state line at Beartooth Pass in Wyoming, 3,337 m (10,947 ft). Most of Montana’s other high ground lies in the parallel ranges of the southwest, such as the Madison, Gallatin and Absaroka ranges, and in the long Bitterroot Range, which divides Montana from Idaho and is one of the longest continuous ranges in the Rocky Mountains. Farther north and east rise island ranges cut off from the main Rockies; the Crazy Mountains, whose Crazy Peak reaches 3,418 m (11,214 ft), stand more than 2,130 m (7,000 ft) above the plains just north of Interstate 90.
Triple Divide Peak and the Lewis Range in Glacier National Park
The Rockies end abruptly in north-central Montana along the Rocky Mountain Front, where mountains give way to prairie with almost no foothills in between. The front is sharpest in the Lewis Range of Glacier National Park, a park of more than 4,100 km² (1 million acres) on the Canadian border, created on 11 May 1910. Its highest summit is Mount Cleveland, 3,190 m (10,466 ft), one of six peaks in the park above 3,000 m.
The mountains here are stacked in the wrong order. In the Late Cretaceous and early Paleogene, roughly 75 to 59 million years ago, a wedge of crust about 12 km thick was pushed some 80 km (50 mi) eastward along the Lewis Overthrust. That shoved Precambrian sediments, laid down in shallow seas between 1.6 billion and 800 million years ago, on top of rock that is far younger, which is why some of the oldest rock in the region now forms the highest peaks.
On the Lewis Range sits Triple Divide Peak, 2,446 m (8,025 ft), where the Continental Divide meets the Northern or Laurentian Divide. Rain falling on its summit can end up in the Pacific, the Gulf of Mexico or Hudson Bay, which is why the peak is called the hydrological apex of North America. The Waterton, Belly and St. Mary rivers on its northern side flow into Alberta and join the Saskatchewan River on its way to Hudson Bay. The Going-to-the-Sun Road, finished in 1932, crosses the divide farther south at Logan Pass, 2,026 m (6,646 ft).
Glacier National Park takes its name from the ice that carved its U-shaped valleys and long lakes such as Lake McDonald and St. Mary Lake. That ice is disappearing: of about 150 glaciers larger than 10 hectares (25 acres) in the mid-19th century, only 25 active glaciers remained by 2010. Our Glacier National Park guide covers the park in more detail.
Three Forks to the Great Falls of the Missouri: Leaving the Mountains
East of the divide, the Missouri River is born at Three Forks in Gallatin County, where the Jefferson, Madison and Gallatin rivers meet. Meriwether Lewis named the three in late July 1805 after President Thomas Jefferson, Secretary of State James Madison and Treasury Secretary Albert Gallatin, and the confluences are now inside Missouri Headwaters State Park. From there the Missouri flows north through a string of reservoirs, including Canyon Ferry, Hauser and Holter, toward the city of Great Falls.
At Great Falls the river drops off the edge of the mountain zone in five waterfalls spread along a 16 km (10 mi) stretch: Black Eagle Falls, Colter Falls, Rainbow Falls, Crooked Falls and Big Falls, the tallest at 26.5 m (87 ft). In all, the river falls 187 m (612 ft) from the first fall to the last, 57 m of it in vertical plunges. The falls were a hard obstacle for the Lewis and Clark Expedition in 1805, which had to carry its boats around them overland, and they were put on the territorial seal and, in 1893, on the state seal. Hydroelectric dams, among them Black Eagle, Rainbow and Ryan, now stand along this stretch.
The falls owe their setting to the last ice age. Between about 15,000 and 11,000 BCE the Laurentide ice sheet blocked the Missouri and backed it up into Glacial Lake Great Falls, which reached a depth of 183 m (600 ft) over the site of the modern city. When the ice retreated, around 13,000 BCE, the lake drained in a catastrophic outburst that cut the Shonkin Sag, a meltwater channel about 160 km (100 mi) long and 150 m (500 ft) deep.
The Missouri Breaks, Fort Peck Lake and the Yellowstone Badlands
Below Fort Benton the Missouri cuts down into the plains through the Missouri Breaks, a strip of badlands, steep bluffs and pale sandstone cliffs where the land seems to “break away” toward the river. The stretch from Fort Benton to the Fred Robinson Bridge was named a National Wild and Scenic River in 1976, and in 2001 the surrounding 1,526 km² (377,000 acres) became the Upper Missouri River Breaks National Monument. The Lewis and Clark Expedition passed through in 1805, and the painter Charles M. Russell later used the Breaks as a model for many of his paintings.
Farther east the Missouri spreads into Fort Peck Lake, the largest body of water in Montana by surface area at about 990 km² (245,000 acres). The U.S. Army Corps of Engineers built Fort Peck Dam between 1933 and 1940; it is 6.4 km (21,026 ft) long and the largest hydraulically filled dam in the United States. The reservoir stretches 216 km (134 mi) through central Montana, and its twisting arms give it a shoreline of some 2,450 km (1,520 mi). Nearly all of it is surrounded by the Charles M. Russell National Wildlife Refuge. Below the dam the Milk River joins from the north, and the Missouri River, 3,767 km (2,341 mi) long in all, carries on into North Dakota and eventually the Mississippi north of St. Louis.
To the south, the Yellowstone River enters Montana near Gardiner from Yellowstone National Park, passes through Paradise Valley to Livingston and then runs northeast past Billings, Miles City, Glendive and Sidney. It is about 1,080 km (671 mi) long, drains roughly a quarter of the state, and has no dam on its main stem, making it the longest free-flowing river in the contiguous United States. Its major tributaries include the Bighorn, Tongue and Powder rivers. Near Glendive, Makoshika State Park protects more than 45 km² (11,000 acres) of badlands, its name from the Lakota for “bad land”. Its rocks belong to the Hell Creek Formation, which has yielded Triceratops fossils, including a 1.7 m (5.5 ft) skull dug up in 1991.
Flathead Lake, the Clark Fork and the Kootenai: Montana’s Lowest Ground
West of the divide every river ends in the Columbia. The Clark Fork rises as Silver Bow Creek near Butte and flows northwest past Missoula, where the Blackfoot and Bitterroot rivers join it, and then on into Idaho’s Lake Pend Oreille. It carries more water out of the state than any other river. Between about 15,000 and 13,000 years ago, as the ice sheets made their final advance, a lobe of the Cordilleran ice sheet dammed the Clark Fork near the Idaho border and backed up Glacial Lake Missoula, a lake of about 7,770 km² (3,000 sq mi) holding half as much water as Lake Michigan. Each time the ice dam broke, the lake drained in a catastrophic flood that scoured the Channeled Scablands of Washington. Giant ripple marks 8 to 15 m high still cover the floor of the Camas Prairie, where the old lakebed is a National Natural Landmark.
To the north, the Flathead River feeds Flathead Lake, 11 km (7 mi) south of Kalispell. The lake is about 48 km (30 mi) long and 26 km (16 mi) wide, with a maximum depth of 113 m (371 ft), and it is a remnant of Glacial Lake Missoula. Kerr Dam at its outlet near Polson, built in the 1930s, slightly raised its level and controls the top 3 m (10 ft) of the lake; the Confederated Salish and Kootenai Tribes bought it in 2015. Although Fort Peck Lake covers more area, Flathead Lake holds more water because it is much deeper.
The last river on the way down is the Kootenai, which flows into Montana from British Columbia. Libby Dam holds it back as Lake Koocanusa, a reservoir that reaches 130 km (81 mi) north across the Canadian border. Below Libby the river drops over Kootenai Falls, the largest undammed waterfall in Montana, then turns northwest at Troy and crosses into Idaho. That crossing, at about 549 m (1,800 ft), is the lowest point in the state, some 3,355 m below the top of Granite Peak.
The Yellowstone, which ties the southern mountains to the eastern plains, has its own story in our Yellowstone River guide.