__, BUTTE TO THE SNAKE PLAINS. 371 



At Ross Fork is the agency of the Fort Hall Indian reservation, a 

 tract of land set aside by Government for portions of the Bannock and 

 Shoshone tribes. These Indians, who Dumber 3,000 to 4,000, are peace- 

 ful and largely devoted to agricnltnral pursuits, raising hay which they 

 sell to cattle owners whose herds graze on the neighboring hills. 



Pocatello, near the southern edge of the Indian reservation, is at the 

 junction with the Oregon Short Line which runs westward through 

 Idaho to Portland, Oregon. It is on the Portneuf river, where it de- 

 bouches from a narrow valley between rounded hills of Paleozoic rocks, 

 partly tilled by very recent Hows of basalt, which are readily visible 

 from the train as it ascends to the more open valley of Marsh creek. 



EXCURSION TO SHOSHONE FALLS. 



THE SNAKE PLAINS. 



By S. E. Emmons. 



The valley of the Snake river presents a most interesting study to 

 the vulcanologist. From its source in the mountains around the Yel- 

 lowstone Park to its junction with Clarkes fork of the Columbia, a 

 distance of about 800 miles (1,287 km.), the rocks which environ it arc 

 mostly recent eruptive rocks or actual lavas. The Columbia river, 

 formed by the junction of these two great streams, flows westward 

 across the lava plains of eastern Oregon for about 120 miles (193 km.), 

 and then debouches on to the lowlands of the Pacific coast, through 

 the stately portal of the Cascade mountains, where, on either side, 

 walls of basalt rise to 3,000 feet (914 in.) almost vertically, and at a 

 little distance north or south the great extinct volcanoes of the Cas- 

 cade range raise their snow-capped summits to altitudes of 10,000 to 

 14,500 feet (3,000 to 4,420 m.) above sea level. This interesting region 

 has not yet been systematically surveyed and the little that is known 

 of its geology has been obtained by reconnoissances of individuals and 

 small exploring parties. 



The Snake plains, properly speaking, occupy an area, whose dimen- 

 sions are not accurately known, extending from the sources of the 

 river some 250 miles (400 km.) slightly south of west, in its broader 

 portion nearly 100 miles (1(50 km.) wide. This area, for the most part 

 practically a plain of basaltic lava, is incidentcd here and there by low 

 hills, either some slight preexistingelevation of underlying older rocks, 

 or inequalities in the lava itself, but contains no high mountains. A 

 general depression, or area without high mountains, extends westward 

 beyond the valley of the Snake, and on the same general line, to 121° 



