Physical Geography

Montana lies in two major physical regions of the United States: the Rocky Mountains and the Great Plains.

The Rocky Mountain region spans the western two-fifths of the state and consists of more than 40 ranges. They trend northwest-southeast but occasionally join in complex knots. Capped by peaks of 8,000 to almost 13,000 feet (2,440 to 3,960 m), the ranges vary from low, rounded chains to ones of rugged alpine beauty.

Lewis and Clark Range, in the north, forms the majestic, glacier-carved backbone of Glacier National Park. Fringing most of the Idaho-Montana border is the Bitterroot Range. Its southern crest line, like that of the Lewis and Clark Range, forms part of the Continental Divide. Montana's highest point is Granite Peak, which reaches 12,799 feet (3,901 m). It lies in the Absaroka Range a short distance northeast of Montana's part of Yellowstone National Park. Also in the Rockies is the lowest point in the state—the valley of the Kootenai River at the Idaho border. Its elevation is about 1,800 feet (549 m).

In the northern part of the Rockies, other ranges include the Cabinet Mountains and the Swan and Mission ranges. In the central section are the Big Belt Mountains and the Garnet and Anaconda ranges. In the southern part are the Pioneer Mountains and the Ruby, Madison, and Gallatin ranges.

The Great Plains region, sometimes called the Missouri Plateau, lies at elevations of roughly 2,000 to 5,000 feet (600 to 1,520 m) and stretches eastward from the Rockies over the rest of Montana. This region consists mainly of rolling to rough grassy plains. There are also badlands, buttes, high mesas, steep-sided river valleys, and isolated mountains and ranges that lie away from the main body of the Rockies. Among the mountains are the Little Rocky, Bears Paw, and Big Snowy.

Montana's rivers drain to the sea by way of three major basins—westward in the Columbia basin to the Pacific Ocean, eastward in the Missouri-Mississippi basin to the Gulf of Mexico, and northward in the Saskatchewan-Nelson basin to Hudson Bay.

Most of the state is drained by the Missouri River. It is formed by the junction of the Jefferson, Madison, and Gallatin rivers in the southwest and flows northward through mountainous terrain in deep gorges and over numerous falls. On the Great Plains, the Missouri flows eastward into North Dakota. Among the river's main tributaries are the Teton, Marias, and Milk rivers from the north and the Musselshell and Yellowstone rivers from the south. Feeding the Yellowstone are the Bighorn, Tongue, and Powder rivers. The only other major streams are the Clark Fork, Flathead, and Kootenai rivers in the northwest.

Dotting the mountains are many natural lakes, including numerous small glacial tarns at high elevations. The largest lake is Flathead Lake, with an area of 197 square miles (510 km 2 ). Reservoirs, created mainly as part of the Missouri River Basin project, predominate on the Great Plains. The largest is Fort Peck Lake, impounded by Fort Peck Dam. Other reservoirs include Lake Elwell and Fresno Reservoir on the plains, and Canyon Ferry and Hungry Horse reservoirs in the mountains.

Montana's climate varies enormously, mainly because of elevation differences within the state and the barrier effect of the mountains. East of the Rockies the severe continental climate of interior North America prevails, west of the Rockies the more temperate maritime climate of the Pacific Northwest. Thus, the western valleys have milder winters and cooler summers than do the eastern plains.

On the plains, winters are long and cold. January averages vary from about 8° to 26° F. (-13° to -3° C.), the coldest area being the northeast. There are many days with temperatures below 0° F. (-18° C.). Blizzards periodically strike the state, but few of them pass westward over the Rockies. Occasional warm periods come to the plains with chinook winds from the mountains. Summers on the plains are warm to hot, July temperatures averaging about 60° to 75° F. (16° to 24° C.); days are hot, nights cool.

Precipitation varies locally. On the plains it comes mainly during early summer and ranges from 10 to 20 inches (250–500 mm). Northwestern valleys receive as much as 35 inches (900 mm); the mountains, up to 100 inches (2,540 mm). Snowfall, too, is highly variable, ranging from as little as 20 inches (500 mm) on the plains to 300 inches (7,620 mm) in the mountains. Droughts occur occasionally. Hailstorms and tornadoes are among the destructive storms.

Great coniferous forests of pine, fir, and spruce cover the slopes of the western mountains. About two-thirds of the timberlands are of commercial value; most are federally controlled. The forests make up one of hte chief economic resources of the western part of the state.