INFLUENCE OF THE FORESTS ON WATER SUPPLY. 77 



portions of the ridges and which has sunk into the cracks and crevices 

 of the strata to become visible again at lower levels. A very large 

 proportion of this water comes from the snow which falls in the zones 

 of the SubaJpine Fir and the Crest Line. The slower the snow melts 

 here, and by far the larger part of the precipitation these zones receive 

 comes in the shape of snow, the higher will be the upper level of the 

 water line and the more will the annual amount discharged by the 

 springs be equalized. 



The amount of water held back in the humus and top soil is immense. 

 In the two zones above mentioned there is but a small deptli of this, 

 but in the White Pine Zone it is very thick. This section is the great 

 water reservoir of the Coeur d'Alenes. Not only does it hold back 

 great quantities of water by its absorbtive power, but the denseness 

 of the forest growths prevents direct evaporation from the surface, and 

 the widely spreading rootlets, together with the other multitudes of 

 obstacles it interposes to the free flow of water in its heavily wooded 

 canyons and bottoms, hold back great volumes. When a fire devastates 

 a region here, these conditions are changed. The sponge of humus is 

 destroyed; the mold in the top soil is burned oh, leaving behind the 

 siliceous portions which do not long retain water, and the shade is 

 gone, exposing the ground to the direct rays of the sun with their 

 baking and desiccating power. When spring comes, the snow that 

 has fallen upon the burned-over areas in any of the forest zones melts 

 with great rapidity. As there is nothing to hold back the water until 

 its absorption into the soil has taken place, it rushes off on the surface 

 in torrents to the plains below. The small quantities that sank into 

 the soil have drained away when summer comes, and a scarcity is the 

 consequence. It will therefore readily be seen that if the mountain 

 streams or lakes are ever to be utilized as reservoirs for water to irri- 

 gate the plains areas it will be necessary rigorously to preserve the 

 primary reservoirs — that is, the forests. 



It is probable that but for one circumstance connected with the 

 climatic conditions of the Coeur d'Alene forest areas there would long 

 since have been felt a very severe scarcity of water in the summer sea- 

 son throughout the regions where fires have exterminated any consider- 

 able portions of the growing timber. The feature referred to is the 

 absence of frosts in the ground during the winter months— a condition 

 which prevails even at elevations above 2,400 meters (7,900 feet). 

 Owing to this the lower surface of the snow melts slowly all winter, 

 and the weight of the heavy superincumbent mass pressing down firmly 

 on the soil holds back the water and compels its absorption. 



Manifold other evils arise from the destruction of the forests. There 

 are the snow slides that imperil life and property with every recurring 

 spring; avalanches of rock and dirt that are loosened and slide down 

 the steep hillsides to the bottoms of the valleys; inundations in the 

 mountain regions and along the courses of the rivers through the plains ; 

 sand, gravel, and bowlders washed down the valleys and spread out 



