Idaho

I

Introduction

Idaho, state in the western United States, forming the eastern section of the Pacific Northwest. Idaho is an area of striking physical diversity and natural beauty. The state’s many natural resources have long been the basis of its economic output and development, and they remain a key to its future progress.

Idaho is primarily a mountainous state; much of it is covered by the Rocky Mountains. High, often snowcapped peaks, broad expanses of plateaus and upland slopes, and some of the finest forestlands in the United States occupy central and northern Idaho. The mountains of the central portion of the state have long formed a barrier to communication between north and south and between east and west. North of these mountains lies a narrow section known as the Panhandle, noted for its numerous lakes and forests and abundant mineral resources.

South of the central mountains and in contrast with the rest of the state is the Snake River Plain. The plain, which is the dominant feature of southern Idaho, curves across the width of the state as a broad treeless expanse of land. It includes the most densely and most sparsely settled sections of the state. The plain includes most of the state’s principal cities and accounts for much of Idaho’s farm output, but it also includes some of the most desolate areas in the Pacific Northwest. Sheets of hardened lava, volcanic craters and cinder cones, and desolate crags and pinnacles form an almost totally barren landscape. Nevertheless, even these desolate areas are not without economic value, for they attract numerous tourists and contain some mineral wealth.

Economic development has proceeded at a rapid pace in Idaho since the 1940s. Agriculture, along with other primary activities, continues to be the basis of the economy, but gains have been made in manufacturing, particularly in food processing, the manufacture of wood products, and high-technology industries. Tourism and recreation are also important sources of income. Boise is Idaho’s capital and largest city.

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Idaho entered the Union on July 3, 1890, as the 43rd state. Its name was for many years popularly held to be a Native American word meaning “gem of the mountains.” However, some believe the name was actually coined in 1860 by white politician George M. Willing, an unsuccessful candidate for congressional delegate from the mining region of Pikes Peak in Colorado. He proposed Idaho as the name for the Colorado territory, but it was rejected when it was revealed that the name was not a Native American word. But the name took hold in the mining regions of what was to become Idaho, and the Congress of the United States designated the territory with the name when it was formed in 1863. The popularly accepted meaning of the word Idaho gave rise to the state’s nickname as the Gem State. Idaho also is known as the Potato State, after its leading crop.

II

Physical Geography

Idaho, the 14th largest state in the Union, has an area of 216,445 sq km (83,570 sq mi) including 2,132 sq km (823 sq mi) of inland water. In shape, Idaho consists of a broad rectangular area in the south, based on the line of latitude 42° north, and a long narrow strip in the north that is known as the Panhandle. The state has a maximum length from north to south of 777 km (483 mi), and it varies in width from 496 km (308 mi) along its southern border to only 72 km (45 mi) in the Panhandle. The mean elevation is about 1,500 m (5,000 ft). The federal government controlled 65 percent of Idaho’s total land area in 2002.

A

Natural Regions

Idaho can be divided into four natural regions, or physiographic provinces, each of which is part of a larger physiographic region of the United States. The four natural regions are the Northern Rocky Mountains, Middle Rocky Mountains, Columbia Plateau, and Basin and Range province. The Northern and Middle Rockies are parts of a larger physiographic division, the Rocky Mountain System. The Columbia Plateau and the Basin and Range province are part of the larger Intermontane Plateaus.

The Northern Rocky Mountains occupy more than half of Idaho. In central Idaho the Salmon River Mountains and Clearwater Mountains form a vast, geologically complex highland mass. The Salmon River Mountains have a maximum elevation of 3,152 m (10,340 ft), at Twin Peaks, and the Clearwater Mountains attain elevations of more than 2,400 m (8,000 ft). Southeast of the Salmon River Mountains, Borah Peak, or Mount Borah, the highest point in Idaho, rises to 3,859 m (12,662 ft) in the Lost River Range. Other ranges in the southern part of the region are the Sawtooth and Pioneer mountains, which rise to 3,681 m (12,078 ft) at Hyndman Peak. To the east the Bitterroot Mountains forms a high, rugged barrier along the Idaho-Montana state line. In the Panhandle the mountains decrease in elevation, but they are no less rugged.

Deep canyons, rocky gorges, and innumerable ridges make transportation difficult throughout the region. There are few good passes through the mountains, especially the Bitterroot Mountains and Salmon River Mountains. Most of the mountains are heavily forested. This natural region is the source of most of Idaho’s mineral output.

The Middle Rocky Mountains occupy a belt along the Idaho-Wyoming boundary. The chief ranges include the Aspen, Bear River, Caribou, Preuss, and Snake River ranges. They attain heights of more than 3,000 m (10,000 ft) and run from north to south.

The Columbia Plateau, in Idaho, is diverse, and includes the Snake River Plain, part of the Owyhee Uplift, and small portions of the Seven Devils, Craig Mountain, and Palouse sections.

The great crescent-shaped Snake River Plain descends from 1,800 m (about 6,000 ft) above sea level near the Wyoming border to less than 760 m (2,500 ft) at the Oregon border. Thick lava flows cover or underlie most of the plain, which has numerous thermal springs, cinder cones, high basaltic cliffs, and other features of volcanic origin. The Snake River lies near the southern edge of the lava flows. The plain is far wider than the river valley, and it extends northward for as much as 80 km (50 mi) from the river. Large irrigated areas support much of Idaho’s agriculture. Most of the state’s population lives in the Snake River Plain.

The Owyhee Uplift occupies the southwestern corner of Idaho. The main features of this section are the rugged Owyhee Mountains, high basaltic plateaus, and the deep Bruneau River canyon. The Seven Devils, Craig Mountain, and Palouse sections occupy a small portion of northern Idaho east of the part of the Snake River that forms the state’s western border. They contain a few small but productive areas of farmland, especially in the Lewiston area. In the Palouse section there are gently sloping hills that have a distinctive dunelike appearance. They were formed at the close of the Ice Age about 10,000 years ago by the deposition of fine, wind-blown deposits called loess.

The Basin and Range province occupies a small area of southern Idaho between the Middle Rocky Mountains and the Snake River Plain. The principal ranges are between about 1,200 and 1,800 m (about 4,000 and 6,000 ft) above sea level and run generally from north-south. Small valleys between the ranges, where water for irrigation is available, are used for farming, and the mountain slopes are used for livestock grazing.

B

Rivers and Lakes

The Continental Divide, which separates streams draining to the Pacific Ocean from those draining to the Gulf of Mexico and the Atlantic Ocean, follows part of the Idaho-Montana state line in the southern part of the Bitterroot Mountains. Consequently, nearly all the rivers in the state drain toward the Pacific. Most of Idaho lies within the drainage basin of the Columbia River system. The Snake River, which is the chief river in southern and central Idaho, follows a crescent-shaped course for about 790 km (about 490 mi) across southern Idaho. It then swings northward along the Idaho state line and joins the Columbia River in Washington. Major tributaries of the Snake River in Idaho are the Boise, Payette, Clearwater, and Salmon rivers. The main tributaries of the Columbia River in northern Idaho are the Saint Joe and Coeur d’Alene rivers, which form the Spokane River at Coeur d’Alene Lake. The Kootenai, Clark Fork, and Pend Oreille rivers flow for part of their length in Idaho. Small areas in the south drain southward into the Great Basin.

The rivers of Idaho are widely used for irrigation and hydroelectric power production, especially in the south. However, the Snake River is used for navigation as far upstream as Lewiston. Major road and railroad routes follow the principal valleys, although canyons along the Snake, Salmon, and other rivers pose major problems for road builders. The deepest gorge is Hells Canyon, also called Seven Devils Canyon, Box Canyon, Grand Canyon of the Snake River, or Snake River Canyon. The canyon, the deepest in the United States, has a maximum depth of 2,400 m (about 7,900 ft). The river at the point it leaves the state is the lowest point in Idaho, at 216 m (710 ft) above sea level.

Lakes are abundant in Idaho, and most of the large ones are located in the Panhandle. The state’s largest lake is Pend Oreille Lake, which covers 344 sq km (133 sq mi). It is fed by the waters of Clark Fork and is drained by the Pend Oreille River. Other large natural lakes are Coeur d’Alene Lake, Priest Lake, and the Upper and Lower Payette lakes. Reservoirs created by irrigation and power dams include the Dworshak, American Falls, Cascade, Palisades, Brownlee, Blackfoot, Lucky Peak, Island Park, Anderson Ranch, and Arrowrock.

Idaho’s abundant water resources play a key role in the state’s economy because much of the state’s agricultural production is dependent on irrigation. About 1.2 million hectares (about 3.1 million acres) of cropland in Idaho are irrigated. This irrigated area covers 53 percent of all cropland and accounts for an even larger share of Idaho’s income from agricultural production. The Snake River and its tributaries are the chief source of surface water. Dams and reservoirs even out the irregular flow of the rivers by holding back snow meltwater in early spring and summer and by releasing it for use in the dry summer months. Underground water from wells is increasingly being used for irrigation projects in the Snake River Plain.

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