32 BULLETIlSr 61, V. S. DEPAETMENT OF AGEICULTUEE. 



of the equation is the only one which admits of approximate quantitative statement, 

 and figures for this have aheady been given. ^ 



Of the ions, sodium and potassium are of most interest. These constitute 19.4 

 per cent of the saline material. Potassium may be taken as 20 per cent of the com- 

 bined weight of sodium and potassium. Applying these proportions to the 3,061,138 

 tons of salines for the four basins gives 593,860 tons of sodium and potassium, and 

 118,772 tons of potassium as the annual "crop" for approximately 95,000 square miles 

 of the basin. 



The figures given in the preceding represent the rate of accumulation under present 

 conditions. The humid conditions of the Quaternary must have produced a much 

 greater rate of accumulation than at present. The greater area of lake surface during 

 Quartei'nary times would give less land surface for chemical denudation. For the 

 Lahontan and Bonneville Basins it has been shown that for one unit of lake area there 

 were 3.5 units of basin area. For the 95,000 square miles under consideration this 

 ratio would give 74,027 square miles of land and 20,973 square miles of lake surface. 

 If we assume that the rate of accumulation equaled the present rate for the Tuolumne 

 River watershed, the above area of land surface would yield a "crop" of 13,650,000 

 tons per annum, or about four times the present rate of accumulation. While these 

 results are no doubt crude, they at least give us some idea of the enormous amounts 

 of salines that must have been discharged by the rivers of Quaternary times into the 

 Quaternary lakes. 



SALINE DEPOSITS. 



To avoid repetition, this subject is presented under the following heads: Nitrates; 

 Borates; Alum; Alunite; Crusts and Efflorescences; Playa Deposits; Deposits Result- 

 ing from Desiccation of Lakes; Buried Deposits of Salines; Salines in Present Lakes; 

 Calcareous Deposits about the Shores of Present Lakes; Potash-rich Minerals; and 

 Gypsum. 



NITRATES. 



Gale 2 has summarized the occurrence of nitrates in the Great Basin region. From 

 his work I give below some of the principal facts. 



Nitrates have been reported in Utah, in the vicinity of Marysvale, Monroe, and 

 Greenwich Canyon, and Grass Valley; in Nevada, in the \dcinity of Lovelock, in north- 

 western Washoe County near Leadville, and in the canyons bordering the west side 

 of Railroad Valley; in California, in the vicinity of the Calico Mountains, in the 

 region northeast of Salton, along the Amargosa River near Tecopa, and in the vicinity 

 of Death Valley, Searles Lake, and Danby Lake. The compounds reported are 

 potassium, sodium, magnesium, and calcium nitrates. Potassium nitrate is the com- 

 pound most often found. The deposits are of three types — cave, playa, and as efflo- 

 rescences. Most of the Nevada deposits are of the cave type. They occur as veins, 

 stalactites, and crusts in deposits protected from the action of surface waters. In 

 playas, the nitrates are mixed with other salines. Occasional efflorescences of nitrates 

 are found. The deposit occurring south of Tecopa, Cal., and along the Amargosa 

 is of this t^'pe. The nitrates of the basin region are either leached from the soils or 

 originate from the decaying organic matter accumulating in the caves. Gale is of the 

 opinion that probably a majority of the nitrate deposits result from the decomposition 

 of bat or similar guano in caves, or crevices in the rocks. 



Nitrates have been reported in small amounts in river and lake waters. Van 

 Winkle and Eaton report the nitrate radical in 18 river waters out of some 30 examined 

 in California. The average content for the Owens River is 1.7 paxts per million. This 

 is equivalent to 0.5 per cent of the anhydrous residue. A more extended search for 

 this radical would, no doul)t, show it present in small amounts in most of the river 

 waters of the basin. The origin of nitrate in river water is due to the leaching action 

 of rain water on soils. Owens Lake contains 948 parts per million of nitrate radical.^ 

 J. G. Smith reports traces of nitrates in all the waters from the southern Oregon lakes 

 which he examined. I have no doubt that this radical, in small amounts, could be 

 found in other basin lakes. In the analysis of the soluble material of basin soils 



1 The mean annual nm-ofl for the basin region was approximately determined to be 1.06 inches of rainfall 

 If we assume the saline content to be 62.7 parts per 100,000 (the mean saline content of California rivers for 

 semiarirt conditions), the saline content in the run-off from 1 square mile is 96,251 pounds. This approxi- 

 mates the figure obtained for the Bonneville basin. On this basis the annual crop of salines for the whole 

 basin would be 10,105,200 tons. The playa, silt and lake area is about 30 per cent of the basin area or 63,000 

 square miles. The concentration of the annual crop of salines on this area would give 164 tons per square 

 mile or a surface crust 0.0012 of an inch thick. 



2 Bui. No. 523, U. S. Geol. Survey. 



» Water-Supply Paper No. 237, p. 122. 



