_Physical Features._--Idaho's elevation above sea-level varies from 738 ft. (at Lewiston, Nez Perce county) to 12,078 ft. (Hyndman Peak, on the boundary between Custer and Blaine counties), and its mean elevation is about 4500 ft. The S.E. corner of the wedge-shaped surface of the state is a part of the Great Basin region of the United States. The remainder of the state is divided by a line running S.E. and N.W., the smaller section, to the N. and E., belonging to the Rocky Mountain region, and the larger, S. and W. of this imaginary line, being a part of the Columbia Plateau region. The topography of the Great Basin region in Idaho is similar to that of the same region in other states (see NEVADA); in Idaho it forms a very small part of the state; its mountains are practically a part of the Wasatch Range of Utah; and the southward drainage of the region (into Great Salt Lake, by Bear river) also separates it from the other parts of the state. The Rocky Mountain region of Idaho is bounded by most of the state's irregular E. boundary--the Bitter Root, the Coeur d'Alene and the Cabinet ranges being parts of the Rocky Mountain System. The Rocky Mountain region reaches across the N. part of the state (the Panhandle), and well into the middle of the state farther S., where the region is widest and where the Salmon River range is the principal one. The region is made up in general of high ranges deeply glaciated, preserving some remnants of ancient glaciers, and having fine "Alpine" scenery, with many sharp peaks and ridges, U-shaped valleys, cirques, lakes and waterfalls. In the third physiographic region, the Columbia plateau, are the Saw Tooth, Boisé, Owyhee and other rugged ranges, especially on the S. and W. borders of the region. The most prominent features of this part of the state are the arid Snake river plains and three mountain-like elevations--Big, Middle and East Buttes--that rise from their midst. The plains extend from near the S.E. corner of the state in a curved course to the W. and N.W. for about 350 m. over a belt 50 to 75 m. wide, and cover about 30,000 sq. m. Where they cross the W. border at Lewiston is the lowest elevation in the state, 738 ft. above the sea. Instead of being one plain formed by erosion, this region is rather a series of plains built up with sheets of lava, several thousand feet deep, varying considerably in elevation and in smoothness of surface according to the nature of the lava, and being greater in area than any other lava beds in North America except those of the Columbia river, which are of similar formation and, with the Snake river plains, form the Columbia plateau. Many volcanic cones mark the surface, but by far the most prominent among them are Big Butte, which rises precipitously 2350 ft. above the plain (7659 ft. above the sea) in the E. part of Blaine county, and East Butte, 700 ft. above the plain, in the N.W.