POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 



9 



Basin river streams may be divided into three types: 



(1) Streams characteristic of the higher mountains. These are short streams which 

 take care of the winter precipitation and carry their waters to the outwash slopes to 

 be distributed by the porous detrital fans. 



(2) Streams, such as the Amargosa, Reese, and Quinn Rivers, which reach main 

 basins but do not carry sufficient water to make a continuous flow, or which reach basins 

 of such magnitude that they can not form permanent lakes. _ 



(3) Streams which supply permanent lakes. The drainage of the Sierra Nevada 

 and Wasatch Mountains supplies practically all of these lakes. Owens, Mono, Carson, 

 Walker, Pyramid, Honey, and the lakes of southern Oregon are typical examples of 

 such lakes in the west; while Great Salt Lake, Utah Lake, and Sevier Lake are in the 

 east and are supplied by the drainage of the Wasatch Mountains. 



A list of these lakes, together with elevations and drainage area of basins, is given in 

 Table VIII (Appendix). 



The proportion of the annual precipitation which appears as run-off varies in different 

 basins. The length of the stream and the character of the watershed, as well as local 

 climatic conditions, determine this factor. The following table summarizes the run-off 

 factor for the Carson, Walker, Truckee, and Humboldt Rivers. 



Proportion of rainfall distributed in the run-off. 



River basin. 



Average 



rainfall, 



mean 



annual. 



Run-off. 



Run-off in 



percentage 



of average 



rainfall. 



Carson .' 



Inches. 

 11.5 

 11.5 



23.82 

 8.12 



10.31 



Inches. 

 6.25 

 2.63 

 9.18 

 0.25 

 ; 1 0. 71 

 \ 2 1. 19 



54.3 



East Fork Walker 



22.8 



Truckee 



38.9 



Humboldt 



3.07 



Whole basin region 



16.80 





2 11. 50 



1 By calculation based upon the total mean annual stream flow, plus an additional amount estimated 

 at one-half the kno^vn amount for the flow of the streams upon which no data are avaUable. 



2 By calculation based on an assumed rate of evaporation of the water from the lakes into which the 

 rivers flow. 



In addition, an attempt has been made to calculate the probable total run-off for 

 the whole basin region. The first calculation is based upon the total mean annual 

 stream flow plus an arbitrary amount for the flow of the streams upon which no data 

 are available. The additional amount has been estimated as one-half of the known 

 amount. This gives a run-off equivalent to 0.71 inch, or 6.8 per cent of the total 

 precipitation. The second calculation is based on an assumed rate of evaporation 

 of the water from the lakes. The total area of lake surface is 4,196 square miles. 

 Assuming an annual evaporation of 60 inches gives an annual run-off of 1.19 inches, 

 or 11.5 per cent of the average annual precipitation. The latter figure is un- 

 doubtedly high, as in the southern half of the Great Basin the run-off is practically 

 zero. For instance, the Amargosa River is a typical desert stream and flows only 

 at rare intervals and during periods of excessive precipitation. At other times water 

 occasionally rises in springs from the dry bed, flows a short distance, and then 

 sinks. The run-off for this whole southern area must be less than 1 per cent. 



As more than 50 per cent of the area of the Great Basin is flat, or characterized by 

 slopes of low angles (0 to 5°), it may be assumed that for areas of this nature, receiv- 

 ing 10 inches or less mean annual rainfall, the run-off is practically zero. For the 

 basin ranges themselves the run-off can not be in excess of 50 per cent, and it is prob- 

 ably much less. Much of this run-off is absorbed by the outwash slopes. We may 

 take the Humboldt River as an example to illustrate this point. This stream rises 

 in the Ruby Range, upon which there is considerable precipitation. At Oreana the 

 mean annual flow gives a run-off of 0.25 inch (drainage area, 13,800 square miles), or 

 3.07 per cent of a mean annual rainfall of 8.12 inches. This means that most of the rain- 

 fall in the mountains along the course of the Humboldt is absorbed before it can reach 

 the main river. 



The basin region may be divided into mountain area, outwash area, and combined 

 silt and playa areas. These approximate 50, 20, and 30 per cent, respectively, of the 

 total area. An inspection of the precipitation tables given on a preceding page shows 



