Idaho

C

Climate

The plains, basins, and valleys of Idaho generally have a dry climate, with cold winters and hot summers. Cooler and generally wetter conditions prevail in the mountains throughout the year.

C

1

Temperature

In winter, temperatures in western Idaho are generally higher than those in eastern Idaho. Average January temperatures in southern Idaho range from -2° C (29° F) at Boise to about -8° C (about 18° F) at the eastern end of the Snake River Plain. In the mountains of the southeast, near Yellowstone National Park, the January average is only about -11° C (about 12° F). Temperatures of extreme cold rarely occur in Idaho because the high mountains along the eastern border protect the state from the icy blasts of Arctic air that frequently bring bitterly cold weather to the lands east of the Rockies.

In summer southwestern Idaho is the warmest part of the state, with average July temperatures of more than 23° C (74° F) at many places. Lower summer temperatures prevail in the mountains and in most of the Panhandle. In the valleys and plains of Idaho, daytime highs sometimes are in the upper 30°s C (lower 100°s F).

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2

Precipitation

Precipitation (rainfall and snowfall) varies greatly from place to place. It averages between about 200 and 500 mm (about 8 to 20 in) in most valley and plain areas. The high mountains in central Idaho and the Panhandle are the wettest sections, receiving as much as 1,300 mm (50 in) of precipitation a year. Most precipitation falls in the winter months, mainly in the form of snow. Snowfall is especially heavy in the mountains, and the remote areas of the state may be inaccessible for months. The snow melts quickly in western Idaho, but in the colder areas of the state it often lies on the ground for the entire winter.

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D

Soils

The most productive soils in Idaho are the sierozems, or desert soils, that cover sections of the Snake River Plain and other areas. When irrigated, the sierozems can provide abundant crops of potatoes, alfalfa, grain, fruit, and vegetables. Prairie soils are found in the western part of the state, around Lewiston and Moscow. Like the other productive soils of Idaho, the prairie soils developed on loess, or wind-deposited material. However, here too, irrigation is often necessary. The remainder of the state is covered by poor soils. The mountain areas have thin, stony soils that are unsuited to agriculture. Thin, stony, and infertile soils imbedded with fragments of pumice and cinder cover the lava beds in the western Snake River Plain. Wide areas of the lava plains, as in Craters of the Moon National Monument, are devoid of soils.

E

Plant Life

Forests cover 40 percent of the land area of Idaho. Most of the forests are located in the Northern and Middle Rockies, below the timberline at about 3,000 m (about 10,000 ft). Among the trees found in Idaho are species of pine, fir, spruce, hemlock, larch, cedar, and other conifers. Ponderosa pine, a drought-resistant tree, flourishes in areas that receive as little as about 500 mm (about 20 in) of rain a year. The western white pine, or Idaho white pine, is the state tree. It grows in the wetter areas of northern Idaho in magnificent stands. Engelmann spruce usually grows at elevations above the white pine, and at even higher elevations, Alpine fir and mountain hemlock cling to bleak, exposed mountain slopes. Other common conifers are Douglas fir, western hemlock, western red cedar, western larch, lodgepole pine, and lowland, or grand, fir. Quaking aspen is the principal deciduous tree in Idaho and is common in the south, while birch are found in the Panhandle. Much of southern and southwestern Idaho is too dry for trees and is covered by sagebrush and bunchgrass, although cottonwood and box elder trees are numerous along stream courses. Almost three-fourths of the commercial forestland is federally owned. About one-fifth of the forestland is privately owned, and the rest is owned by the state.

Many different mosses, ferns, and wildflowers grow in Idaho. Several varieties of orchid are found deep in the forests, and violets and buttercups dot the mountain meadows in spring and summer. Other flowers include the camas, iris, bitterroot, wild hyacinth, lady’s slipper, larkspur, columbine, and sweet pea. Syringa, the state flower, and mountain laurel, rhododendron, huckleberry, and other flowering shrubs are also abundant. Water-loving plants include water plantain, skunk cabbage, and pond lilies, which are found along streams throughout the state. Fireweed, goldenrod, lupines, sand lilies, and sego lilies are common flowering plants in the dry areas of the state.

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