12 BOTANICAL SURVEY OF THE CCEUR D'ALENE MOUNTAINS. 



in most places overlying the bed rock to au unknown but certainly very 

 considerable depth. This gravel is very permeable to water, and has 

 everywhere a large underflow. 



The multitude of canyons and ravines which branch off from the 

 larger stream valleys in all directions have each a flowing stream at 

 the bottom, which in its turn is supplied by the springs that break out 

 at frequent intervals from the inclosing ridges along their course. 



It has already been remarked that Lake Cceur d'Alene receives the 

 entire drainage from the inclosed Cceur d'Alene areas. The outlet of 

 the lake is the Spokane Kiver. This stream is of great commercial 

 importance to a large extent of country by reason of the water power it 

 furnishes at various points. The stage of water in it depends wholly 

 upon the amount of the annual precipitation within the Coeur d'Alene 

 triangle. Owing to the peculiar situation of the lake, it would be pos- 

 sible to hold back a sufficient quantity of water in it to secure a nearly 

 uniform flow in the Spokane throughout the year. 



At a distance of 11.5 kilometers (7.15 miles) from the lake down the 

 Spokane Kiver is Post Falls. The stream here cuts through a dike 

 of gneissoid or some other variety of metamorphosed magnesian rocks, 

 and forms a fall of about 12 meters (3D feet) in height. By the cutting 

 through of this dike the lake has been drained from its last high stage 

 of water and the slack-water channels of the rivers of the Cceur 

 d'Alene basins created. 



Should it ever become necessary to store a large quantity of water in 

 Lake C<eur d'Alene, it can readily be accomplished by dams at this 

 point, and a nearly uniform stage of water throughout the year be 

 secured for the points below. Such procedure, however, would over- 

 flow all the agricultural lands bordering ou the slack-water portion of 

 the rivers, as they now have only an elevation of 2 to 3 meters ((» to 10 

 feet) above low water. 



The drainage which flows from the Comr d'Alene Mountains outside 

 the inclosed basins is disposed of as follows: The eastern slopes of the 

 inclosing rims of mountains in the east drain partly into the Missoula 

 Kiver and partly into the Clark Fork of the Columbia by the channels 

 of various small tributaries of these streams. The southern slopes of 

 the divide which forms the base of the Cceur d'Alene system in the south 

 drain in part into the North Fork of the Clearwater and in part directly 

 into the main Clearwater. The western slopes of the northern half of 

 the inclosing west rim drain in part into Lake Pend Oreille; south of 

 the lake, and north of Lake Cceur d'Alene, the drainage flows into the 

 upper Spokane plains and sinks as soon as it readies these gravel- 

 covered plains to a depth of about 100 meters (325 feet), whence it 

 probably finds its way into the Columbia direct. South of Lake Cceur 

 d'Alene the waters flow partly into Hangman Creek, a tributary com- 

 ing into the Spokane Kiver just below the city of Spokane, and partly 

 into the Palouse, a tributary of the Snake Kiver. 



