POTASH SALTS AND OTHER SALINES IN THE GEEAT BASIN REGION. 39 



to feed a stream for a portion of the year and the basin receives sufficient water to form 

 a permanent lake. The lakes occupying the Quaternary basins are of this character. 

 Respecting the movement of salines in solution, it will not be out of place to mention 

 the following: Assuming the ideal basin, and considering such a basin supplied by 

 rainfall and not receiving the discharge of any stream, the run-off ground water reaches 

 the central playa and brings with it more or less soluble salts. The ground water which 

 eeeps in from the margins brings in considerable salts. This is shown by the crusts and 

 efflorescences which are continually forming on the marginal portions. The water 

 which comes from springs in the central part of the playa is comparatively free from 

 salts. We would expect that the deeper water would be comparatively free from 

 salines and Only in the case where it flowed up through saline beds would we expect to 

 find much evidence of soluble salts. A not unimportant conclusion may be drawn 

 here and that is that artesian flows in the central portion of a playa, if free from more 

 than nominal amounts of soluble salts, indicate the absence of deposits of salt at depth. 



PLAYAS. 



Desert basins not occupied by perennial lakes may be divided into two groups- 

 mud playas and marshes. The former are playas which are dry and without any great 

 accumulation of underground waters; the marshes are playas noteworthy on account 

 of the accumulation of considerable bodies of underground water and in which the 

 water can be found comparatively close to the surface. For convenience in presenta- 

 tion, I have divided the marshes into two types — marshes in which there is no evidence 

 to show of the existence of a former lake having a level higher than the present siu-face 

 of the playa, and marshes in which there is evidence of a former lake with surface 

 higher than the present level of the playa. Examples of these are as follows: 



Playas. — Most of the smaller desert basins having small drainage area fall into this 

 class. The small playas north of Reno; the Alkali Flat in Gabbs Valley; Sarcobatus 

 Flat, Amargosa region; Big Smoky playa; and the playas near Mina and Luning. 



Marshes (first type). — Rhodes, Teels, Silver Peak, Saline Valley, Fish Lake Valley, 

 Death Valley. 



Marshes (second type). — Columbus, Panamint, Sand Springs Flat, Searles, Railroad 

 Valley, Black Rock Desert, Dixie Valley, Alvord Marsh. 



The list is not complete and it is evident that the line of demarcation is not a sharp 

 one. Changing climatic conditions might be expected to alter the classification. 



MUD PLAYAS. 



Playas of this type can not be looked upon as the locus of important accumulations 

 of salines. The small drainage area and the arid climatic conditions would result in 

 little accumulation of ground water and that would be at considerable depth, well 

 without the zone of possible concentration by evaporation. For example, the playa 

 just east of Mina, Nov., contains two wells close to the western edge of the silt area. 

 One well shows water at 112 feet and the other at 114 feet. The water from these wells 

 is used for railroad and town purposes. This example is, perhaps, not as good a one to 

 illustrate the point as could be desired on account of the fact that the underground 

 water probably drains into Rhodes Marsh some 6 mUes south and 152 feet lower. 

 Ground water may be looked for at varying depths in almost all playas of this type. 

 What salines are present are, however, at the surface, in thin crusts and efflorescences 

 or concentrated within the upper portion of the sUt area in much the same way as was 

 described under the subject of the accumulations of salts in soils. 



Desiccation products at depth in playas of this type are more than otherwise apt to 

 be of slight thickness and dubious value. While it can not be said that lakes did not 

 occupy the playas under the humid conditions of the Quaternary, still it can be said 

 that such lakes must have been very shallow and their saline content left by evapora- 

 tion consequently small in amount. The absence of beach lines and their accumula- 

 tion of gravel about the playa is, in my judgment, sufficient to warrant the assumption 

 that a lake was either not present or was a shallow one of periodic occurrence. 



MARSHES. 



The conditions which pertain to marshes of the first type can best be described 

 by examples. R. B. Dole ' examined the Silver Peak Marsh, Nev. From his accoimt 

 I have taken the main facts. The area is due east of Blair, Nev. The marsh is 32 

 square miles in extent and is in a basin having an area of 550 square miles. Tertiary 

 volcanics and sedimentaries, limestones, slates, and quartzites of Paleozoic age, and 



1 Bui. No. S30E, U. S. Geological Survey. 



