POTASH SALTS AND OTHER SALINES IN THE GEEAT BASIN REGION. 3 



and particularly dealing with the geochemical features, has been made. In order to 

 widen out the field and stimulate prospectors and others to direct their attention to 

 this mineral, the Bureau of Soils, the United States Geological Survey, and the Mackay 

 School of Mines established a joint laboratory for the examination of mineral and other 

 naturally occurring substances suspected to contain potash. The results of the United 

 States Geological Survey investigators have been presented from time to time in 

 bulletins.* 



The results of the work of the Bureau of Soils are, in part, presented in a paper by 

 E. E. Free (The Present and Past Topography of the Undratned Areas of the United 

 States).- The purpose of the present paper is to present a review of the information 

 now available on the subject of the occurrence and origin of the salines of the Great 

 Basin region, as well as the chemical data which have been accumulated by the 

 Bureau of Soils and the Cooperative Laboratory. Naturally a review of the geo- 

 chemical features of a region of this extent will not be complete, but it is believed 

 that such a review will be of value at this time and will indicate quite clearly the 

 lines along which future investigation should be directed. 



For an adequate conception of the geochemistry of a region it is necessary to know 

 the principal facts concerning climatology, topography, geology, the surface and under- 

 ground waters, the* evaporation from ground and surface waters, and the distribution, 

 and chemical character of the rocks. These subjects will be treated in the order 

 stated. 



CLIMATOLOGY. 



The Great Basin is spoken of as an arid region, and just what is the significance of 

 this term may be gathered from the tables in the Appendix. These tables have been 

 compiled from Weather Bureau reports on precipitation and temperature. They are 

 grouped in four divisions; Weather stations in Nevada, weather stations in western 

 Utah, weather stations in the part of the basin region included in Oregon, and weather 

 stations in that part of the basin region included in California. The altitude and 

 mean annual rainfall of each station is given. (See Appendix, Table I.) The average 

 (arithmetical mean) annual rainfall of the stations in each group is, for the Oregon 

 group, 13.59 inches; for the Utah group, 12.8 inches; for the Nevada group, 10.34 

 inches; and for the California group, 4.43 inches. The mean annual precipitation 

 for the entire basin region is 10.31 inches. In arriving at this average the mean for 

 each of the above groups and the area occupied by each group were taken into consid- 

 eration. The variation of the mean annual rainfall with latitude in the basin region 

 may be approximated from Table II. (See Appendix.) Latitude is less a factor in 

 controlling precipitation than altitude. The basins of the Great Basin in general are 

 characterized by a small rainfall. The higher mountains receive a much greater 

 rainfall. An area of high aridity may be marked out, and this includes the Mojave Des- 

 ert, the Amargosa Basin, the Owens, Walker, Mono, Pyramid, Carson, and Black Rock 

 Desert regions. In this area the mean annual precipitation is less than 6 inches. 



An inspection of the weather reports for the basin region shows that some precipi- 

 tation takes place in each month of the year. December, January, February, and 

 March are the usual months of maximmn precipitation; while June, July, August, 

 and September are the months of minimum precipitation. There is, however, much 

 irregularity in the monthly distribution of the rainfall, and the weather charts do 

 not give an entirely clear conception of the situation. Rainfall may be divided into 

 two classes — the normal winter precipitation and the precipitation which usually 

 occurs in August and September. The latter is in the nature of torrential rains and 

 cloudbursts and is conspicuous in the more arid portions of the region. The normal 

 winter precipitation contributes but little run-off in the arid portions, but the August 

 and September precipitations often result in heavy local run-offs which are important 

 agents in the movement of detrital material from the mountains to the plains. Aa 

 might be expected, precipitation of this nature is very irregular. Several years may 

 elapse without sufficient rain to even moisten the desert watercourses. Then a 

 period of heavy rains results in turning such watercoiu-ses into torrents. Stream 

 flows of this nature are of short duration, but the local work of erosion and transpor- 

 tation may be very great. Were it not for these rains, erosion. and deposition in the 

 more arid portions of the basin regiqn would be somewhat inconspicuous and limited 

 principally to the action of wind. The influence of these torrential rains extends 

 over the whole arid region described above. But little study has been made of these 



1 Bui. No. 523, Nitrate Deposits. Bui. No. 530-A, The Search for Potash in the United States; Potash 

 Salts— Summary for 1911. Bui. No. 511, Potash Salts— Their Uses and Occurrence in the United States; 

 Alunite. Bui. No. 530-E, Exploration of Salines in Silver Peak Marsh, Nevada; Press Notice No. 97, 

 Feb. 10, 1913; Prospecting for Potash in Death Valley. 



2 Circ. No. 61, Bureau of Soils, An Investigation of the Otero Basin, New Mexico, for Potash Salts; Cire. 

 No. 62, Bureau of Soils, Report of a Reconnoissance of the Lyon Nitrate Deposit near Queen, Nev/ Mexico. 



