66 DOMESTIC WATER SUPPLIES FOR THE FARM 



nately, within the mountains, springs are numerous, while the 

 valleys are often filled with gravels that yield satisfactory supplies 

 to wells. The rocks themselves are not generally a satisfactory 

 source of water for wells. 



Along the flanks of the Rockies, especially those facing the 

 Great Basin, broad deltas or fans of gravel, washed out by tor- 

 rential streams from the mountains, are often extensively de- 

 veloped. These are commonly saturated in their lower portions 

 by waters supplied from the hills and frequently furnish abundant 

 supplies when penetrated by wells. 



The Great Basin. By the Great Basin is meant that broad 

 tract of desert or semi-desert land lying between the Rocky 

 Mountains and the Sierra Nevadas. It is by no means an un- 

 interrupted trough, but is broken by numerous mountain ranges, 

 ridges and mesas rising sharply above its general surface, often 

 the result of tilted fault blocks of immense size. The rainfall is 

 slight and the rocks of the elevations are commonly bare and shed 

 the scant rain almost as it falls, giving rise to the torrential rushes 

 of water down the numerous canyons that form so characteristic 

 a feature of the region. 



Slight as is the precipitation, however, considerable volumes 

 of water find their way into the broad valley or trough-fillings 

 between the Basin ranges. These unconsolidated sands and 

 silts, partly deposits from the meandering streams of a past geo- 

 logic epoch and partly accumulations in lakes that have long since 

 disappeared, often contain water within easy reach of the surface 

 and form an important source of supply throughout great areas, 

 especially in Utah, Arizona and southern California. In a num- 

 ber of localities, especially in the California district, the deeper 

 waters are under sufficient head to afford flowing wells. Such 

 waters are important sources of supply for municipal, ranch and 

 irrigation purposes. 



The great lava beds of eastern Washington and Oregon and 

 of Idaho fall within the Great Basin Province, and constitute one 

 of the most important water horizons of the West. 



