SKETCH OF THE GEOLOGY AND SOILS OF THE CAHtTILLA BASIN. 



31 



Table 2. — Alkali conlenl of soUs of suceeatwe 

 exposures. Imperial Junction beach. 



emergence from the waters of the Sea. The soils are silts composed mainly of Delta 

 material with perhaps a slight admixture of mountain wash from hills several miles north. 

 Table 2 gives the average alkali content of soils submerged for different lengths of time, 

 as well as several which were not submerged at all. 

 It is apparent that whatever alkali was leached out 

 by the waters of the Sea is almost immediately re- 

 stored on its retreat. This is probably because of two 

 circumstances. First, diffusion of salts through wet, 

 silty soil is very slow, and it is probable that the sub- 

 mergence really produced very little leaching beyond 

 cleaning the actual surface. Second, when the waters 

 retreat they do so slowly and the underground water- 

 table lags (horizontally) considerably behind the actual 

 water-line. It follows that for some time after its 

 emergence the soil is wet and has Salton water continually supplied to it by outward diffusion 

 from the Sea and subsequent capillary rise. Evaporation is intense and the Salton water is 

 brackish. These are ideal conditions for the rapid accumulation of alkali, and it is to be 

 expected that what alkali was leached out by the Sea will be restored, or more than restored, 

 on its retreat. Indeed, as the retreating waters become more and more saline they will leave 



Table 3. — Mechanical analyses of soUs from plantless and planircovered zones, Imperial Jimdion beaeh.^ 



behind them larger and larger proportions of soil alkali, probably far exceeding the alkali 

 present in the soil before submergence. The beginnings of this process can already be 

 detected in the fact that thin salt crusts are beginning to be visible on the soils last exposed. 

 The soils of beaches to be exposed in future will probably have had alkali added rather 



' Analyses are by Dr. C. C. Fletcher and others, of the Bureau of Soib, U. S. Dept. of Agriculture. 



