POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 27 

 Depth of accumulations of soluble salts in soils. 



S-inch rainfall, Imperial Val- 

 ley, Cal. 



8-iach rainfall, 

 Fresno district. 



12-inch rainfall, 



Yellowstone 



Park. 



15-inch rainfall, 



Ventura County, 



Cal. 



20-inch rainfall, 



Grand Falls, 



N. Dak. 



In virgin soils greater part of 

 soluble salts at a depth of 18 

 inches. 1 



Sandy loams 3 to 

 4 feet; coarse 

 sands 4 to 8 

 feet.i 



Heavy soils 4 to 

 6 feet; sandy 

 soils 7 to 11 

 feet .2 



Bulk of soluble 

 salts at 5 feet.i 



Greater part of 

 soluble salts 

 below 3 feet.i 



1 Bui. No. 35, Bureau of Soils, p. 15. 



2 Bui. No. 14, Bureau of Soils, p. 27. 



Two important actions take place in the movement of saline material in soils. 

 Rainfall penetrates the surface soil and percolates down to certain depths. In its 

 passage downward it dissolves a portion of whatever soluble salts may be present and 

 thus leaches the material at the immediate surface. The extent to which this leach- 

 ing would take place would be determined by the proportion of gravity water to water 

 of capillarity and the penetration of the water. This is determined largely by the 

 texture of the soil. With a porous soil this leaching action would be especially notice- 

 able. In the leaching of a soil in the manner described above, it is evident that the 

 more soluble constituents would be first dissolved and carried to the greatest depths. 

 Underground water soon reaches a position of equilibrium which may be within the 

 permanent ground-water level or within the zone close to the surface. Capillarity 

 begins to act. The ground water moves toward the point at which evaporation takes 

 place. It should be noted that when this water reaches its equilibrium position it 

 has dissolved a large amount of salt. When the solution is returned by capillarity 

 these salts are carried with it and deposited at the point where evaporation takes place. 

 Capillarity may not return these salts to the surface, for evaporation may take place 

 below the immediate surface, and the capillary water column may terminate at vary- 

 ing distances from the surface. The height to which the water is raised by capillarity 

 would determine the position of accumulated salts. It has been shown in another 

 place that where ground waters are deeper than 10 feet from the surface little or no 

 evaporation from them takes place. This would indicate that ground waters at depths 

 greater than 10 feet could not be concentrated by evaporation, and consequently there 

 would be little or no opportunity for the separation of salines under such conditions. 



NATURE OF SALINES IN SOILS. 



Calcium, magnesium, sodium, and potassium are the bases almost invariably present. 

 Sodium in almost every instance is the dominating base, while calcium and magnesium 

 are usually the smallest in amount. Potassium is much less than sodium. In the 

 Fallon soils sodium is 12.6 times potassium, while in the Utah soils it is 5.6 times. The 

 acid radicals of chlorine, sulphur, carbon dioxide, nitrogen, and phosphorus are inva- 

 riably present. Chlorides and sulphates usually predominate, although in some soils 

 carbonates and bicarbonates are in greater abundance. The Fallon soils contain sul- 

 phates in greatest amount, while in the Utah soils chlorides are in greatest amount. 

 Bicarbonates are usually present in greater amounts than carbonates. Phosphates 

 and nitrates are present in most cases in traces, although in some exceptional cases 

 nitrates may be present in appreciable amounts. Two Fallon soils showed over 2 per 

 cent nitrate in the total solids. The basin soils would present many variations from 

 the examples given. Borates, for instance, are common in many playas. 



COLLECTION OF SALINES BY SURFACE WATERS. 



RIVER AND LAKE WATERS. 



Rivers being the main collecting agents for gathering salines from a given area and 

 transferring them to the lakes and lake basins, the content and nature of the salines 

 as well as the amount collected can be determined from the analyses of the river 

 waters. It should be noted that the rivers receive a certain proportion of seepage 

 water and consequently the chemical analysis reflects not only the nature of the salts 

 collected from the weathering zone, but also the salts received from underground 

 waters. It is to be regretted that analyses of composite samples taken from basin 

 rivers over long intervals of time are not available. What analyses are given represent 

 single samples. The results must be used with caution. 



The lake waters represent the saline accumulations during present times. It should 

 be noted that certain compounds are precipitating out continuously and consequently 

 the composition of the waters represents an approach to equilibrium conditions for 

 the particular time. Variation in climatic conditions results in the raising and lower- 

 ing of lake levels. The fluctuation in lake levels, together with the continual acces- 



