12 BULLETIN 61, U. S. DEPARTMENT OF AGEICULTURE. 



itself usually with farm crops. On the whole this question has no very important 

 bearing upon our problem and may consequently be dropped. 



In the section on surface waters it is shown that approximately 10 per cent of the 

 mean annual rainfall occurs as run-off in the basin region. The evaporation from lakes, 

 rivers, and transient ponds would be measured by this run-off. The remaining 90 per 

 cent of the mean annual precipitation would be a measure of the evaporation from the 

 surface of the ground, by transpiration of plants, and additions by seepage to perma- 

 manent ground water. It is believed that the addition to permanent ground water 

 is relatively small. 



GROUND WATER. 



A comprehensive study of ground-water conditions in the Great Basin has yet to be 

 made. Some important information pertinent to our subject is available. I have sum- 

 marized the data under the following heads: Ground water in valleys and sinks; in 

 outwash slopes; deep supplies of water; artesian water; springs; and fissure and rock 

 water. 



VALLEYS AND SINKS. 



Ground water is encountered in the Lovelock Valley at depths of 15 to 25 feet.* 

 In this A-alley, after a considerable period of irrigation, ground water has been found 

 at depths of 3 to 6 feet. The figiu-es given in the first statement would represent 

 original conditions, before irrigation took place. This valley is a sUt-filled valley on 

 the lower stretches of the Humboldt River. 



In the Truckee meadows ground water is found at 10 to 12 feet from the surface in the 

 vicinity of Reno, and on the eastern edge of the Truckee Meadows it stands practically" 

 at the surface. In south-central Oregon and the Harney Basin much detailed infor- 

 mation is available. In Chi'istmas and Silver Lake Valleys 46 wells and bores have 

 been reported. ^ Most of these wells are located in the valley and lake silts. The 

 depth to ground water varies from 5 to 49 feet. The average depth of water in all the 

 wells reported is 18 feet. In the Harney Basia 46 wells have been reported.^ The 

 average depth of water in these wells is 21 feet. 



In the Owens River Vallej^, Cal.,^ survey of undergrx)und waters was made by the 

 United States Geological Survey,* and these were found to stand at 2 to 3 feet below 

 the surface over considerable areas. Over the comparatively level valley floor west of 

 Owens Ptiver and included within the 8-foot contour above the river (67 square miles 

 of surface) "the average depth to ground water between 4 and 8 feet extended over 40 

 per cent of this area, and between 3 and 4 feet over 28 per cent. It extends 8 feet in 

 depth over 14 per cent of the area and is 3 feet or less over 18 per cent." 



In the Silver Peak Marsh borings showed ground water at 2 to 12 feet depth and, in 

 the case of many of the bores, water was encountered at 4 feet.^ In the sink in Death 

 Valley water is found a few inches below the salt crust and potholes in the rough salt 

 areas indicate that ground water stands within 1 or 2 feet of the surface over a consid- 

 erable area. On Searles Marsh Dolbear^ reports the brine (over the salt area) to be 

 within one-half inch of the surface. 



At Millers, Nev., wells have been sunk in the desert sands of Big Smoky Valley and 

 water sufficient to supply 160 stamps has been tapped at a depth of 65 feet. The ground 

 water in Big Smoky Valley undoubtedly comes much closer to the surface in the 

 playa southwest of Millers. 



Mina is situated in the valley which forms the south extension of the basin occupied 

 by Walker Lake. It is a typical desert valley. Two wells struck water at 112 and 118 

 feet from the surface. 



Other examples could be cited, but these are sufficient to show that in the playa 

 areas and the low areas generally we may expect to find ground water at no incon- 

 siderable depth from the surface. The area within which the ground water would 

 collect would depend upon the extent of the tributary basin and the rainfall within 

 the basin. 



OUTWASH SLOPES. 



The ground-water conditions in the outwash slopes may best be illustrated by the 

 following quotation^ describing the conditions in the Owens River Valley: 



"The ground-water surface as it approaches the valley floor from the west has an 

 average slope of 90 feet to the mile. The corresponding slope of the ground surface 



J Bui. No. 52, Agr. Expt. Sta., University of Nevada. 

 2 Water-Supplv Paper No. 220, U. S. Geol. Survey. 

 » Water-supply Paper No. 231, U. S. Geol. Survey. 

 < Water-Supply Paper No. 291, U. S. Geol. Survey, 

 s Bui. No. .';.30R, TI. S. Geol. Survey, pp. 7-11. 

 ' En^lneerinK and Mininc; Journal, Feb. 1, 1913, p. 260. 

 7 Water-Supply Paper No. 294, p. 76. 



