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.
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. "Idaho" © Emmanuel BUCHOT, Encarta, Wikipedia
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