POTASH SALTS AND OTHEE SALINES IN THE GREAT BASIN EEGION. 61 



Owens, and Great Salt Lakes, the waters of these lakes are comparatively fresh. Geo- 

 logical evidence goes to show that Lahontan Basin must have been the locus for an 

 accumulation of salines for a long period. The inconsequential surface accumulations 

 of salines in this basin, coupled with the anomalous condition of the present lakes, 

 led Eussell '■ to propose the following hypothesis: 



"After the last great rise of Lake Lahontan there was a long-continued episode 

 during which its basin was more arid than at present. Evaporation during that time 

 is thought to have been equal to precipitation, and the residual lakes were reduced 

 to the playa condition — that is, the remnants of the great lake gathered in the lowest 

 depressions of its basin were annually or occasionally evaporated to dryness, and 

 their contained salts were precipitated and either absorbed by the clays, etc., deposited 

 at the same time, or buried beneath such mechanical deposits. This process may 

 be observed in action in many of the valleys of Nevada in which ephemeral lakes 

 occur. The broad naked playas of Black Kock, Smoke Creek, and Carson Deserts, 

 as well as the level floors of the basins occupied by Pyramid, Winnemucca, and 

 Walker Lakes, are in support of this hypothesis. Should the lakes just mentioned 

 be evaporated to dryness, playas would be left similar to those in neighboring valleys 

 of less depth. 



" It is beneath the level floors of these valleys and lake basins that the more soluble 

 salts once dissolved in the waters of Lake Lahontan are buried. Borings at certain 

 localities might reveal the presence of strata of various salts, but in most cases they 

 are prolsably disseminated through great thicknesses of clay, sand, and other mechan- 

 ical sediments." 



Russell's^ admirable disciission of the freshening of lakes by desiccation, together 

 with the later review in the reference cited above, leaves little to be added. Under 

 the discussion of the present and past rate of accumulation of saline material it was hown 

 that over some 95,000 square miles area a present accumulation of approximately 

 3,000,000 tons of salines per annum is taking place, and that in the humid period of 

 the Quaternary this rate might have been more than four times as large. No even 

 approximate estimate of Quaternary time for the basin has been made, and conse- 

 quently no estimate of the probable quantity of salines can be made.^ That it was 

 large goes without saying. While absolute proof of Russell's hypothesis has not 

 been made, its probability is almost beyond question. If we admit it, the pertinent 

 questions arise: Where are these deposits, and what is their probable value as a 

 Bource of salines? The answer to the first question has been given by Russell. The 

 answer to the second is given in part by the chemical studies of the deposits in Searles 

 and Columbus Marshes, Death and Dixie Valleys, and the partially concentrated 

 solutions of Mono, Owens, and Great Salt Lakes. 



Gilbert shows that Lake Bonneville overflowed and discharged its waters, together 

 with their salines, into river waters which eventually found their way to the ocean. 

 On account of the prevalence of older sedimentaries in the Bonneville basin and 

 the low content of potassium in the brines of Great Salt Lake, together with the above 

 fact, the Bonneville basin is not looked upon as a very favorable place for the discovery 

 of the more valuable salines. On the other hand, Lake Lahontan and the Quaternary 

 basins of the west, central, and southwest parts of the Great Basin have never reached 

 an outlet. The regional rocks are largely volcanic, and consequently these Qua- 

 ternary areas have been looked upon favorably as a possible source of valuable salines. 



If we consider that the present topography of the Lahotan Basin is, in a measure, a 

 counterpart of the topography at the end of the final desiccation period, then we must 

 conclude that the present lakes are holding within their shores the former areas of 

 maximum depression, and, consequently, a part of the saline accumulations is buried 

 in the sediments and beneath the waters of the present lakes. The remainder must 

 be sought for in the mud playas and basins contiguous to the present lake basins. 



An examination of Russell's map of Lake Lahontan at its highest water stage* 

 indicates a division of the lake into five major lakes, Carson Lake, Black Rock Desert, 

 Pyramid, Winnemucca, Walker, and Honey Lakes, given in the order of their mag- 



1 Bui. No. 530 A, U. S. Geol. Survey, p. 16. 



* nth Annual Report, U. S. Geol. Survey, p. 244. 



8 Russell estimates the duration of the post-Lahontan period to be less than 300 years. Gilbert estimates 

 tlia.t at the present rate of accession some 34,000 years would be necessary to account for the sodium chlo- 

 ride iu Great Salt Lake. I have calculated the following: At present rates of accession it would take 

 18,576 years for the chlorine accumulation in Owens Lake; 9,028 years for the chlorine accumulation in 

 Mono Lake (assuming the same per square mile annual rate of accumulation that was determined for the 

 Truckee Basin); 4,529 years for the chlorine accumulation in Pyramid Lake; 840 years for the chlorine 

 accumulation in Walker Lake, and 6,452 years for the nitrate accumulation in Owens Lake. The impos- 

 sibility of determining the average rate of accumulation renders such determinations of little value. 



* Eleventh Annual Report, U. S. Geol. Survey pi. 5, p. 32, and the U. S. Geol. Siu-vey topographic 

 sheets, Granite Range, Nev.; Disaster, Nev.; and Honey Lake, Cal. 



