THE ZOOLOGY OF THE SNAKE PLAINS OF IDAHO. 

 By C. Hart Merriam. 



The basin of the Snake River in Idaho is an undulating, 

 sage-covered plain, stretching completely across the State in its 

 widest part. It is crescentic in shape (with the convexity to 

 the south) and measures about 600 kilometers (375 miles) in 

 length by 120 to 100 kilometers (75 to 100 miles) in average 

 breadth. Its boundaries on the north and east are everywhere 

 sharply defined, consisting of rugged mountains rising more or 

 less precipitously from the plain. In several places these 

 mountains project southward in parallel ranges, like so many 

 fingers, alternating with northward extensions of the plains, 

 which occupy the valleys between them. Such valleys are 

 those of Birch Creek and Lemhi River, Little Lost River^ 

 and Malade or Big Wood River. On the .south and west 

 the Snake Plains are not so well defined, passing south 

 ward into Utah and Nevada between irregular ranges of 

 mountains, and westward and northwestward into Oregon 

 and Washington, where they are continuous with the 

 Malheur Plains and plains of the Columbia. The altitude of 

 the basin along the course of Snake River is about 1,800 

 meters (nearly 6,000 feet) at the eastern end, and less than 900 

 meters (3,000 feet) at the western, and its sides rise on the 

 north and south to the altitude of 2,000 or even 2,150 meters 

 (approximately 6,500 to 7,000 feet), forming a broad trough 

 whose general direction is east and west. 



The dominant feature of the Snake River basin is sage 

 plains— rolling, uninterrupted plains, rising so gradually from 

 the bottom of the basin as to appear almost level, and stretch- 

 ing away in every direction as far as the eye can reach. The 

 plains are everywhere arid. The few streams that reach 

 Snake River by a surface course usuallv flow in lower channels 

 and do not water the region on either side. 



The surface rock which crops out here and there over the 

 sage plains proper is dark basaltic lava. It appears in the 

 form of irregular masses or beds, extensive lava flows, and in 



