POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 63 



one lake to the other, and perhaps the assumption that there was no considerable flow 

 from one lake into the other is the nearest to the fact. This would lead us to conclude 

 that in each of these basins we might expect salines at depth. 



The present depth of Pyramid and Walker Lakes, needless to say, would preclude 

 exploration work in these localities. The profiles of Pyramid, Winnemucca, Mono, 

 and Walker Lakes are shown in figure 7. These profiles show the deepest portions of 

 the lakes to be in the central part or away from shores or inlet streams. Topographic 

 evidence goes to show that the saline deposits in Black Rock Desert must'have been 

 spread over a great area and must have been relatively thin. The difficulty of pros- 

 pecting or exploring has been commented upon. 



Carson Lake is comparatively shallow and would not offer serious obstacles to 

 exploratory work. The fact that the Carson Sink receives the drainage of both the 

 Humboldt and the Carson Rivers, each of which drains relatively large areas, as well 

 as the extent of the Quaternary lake, makes this basin comparatively attractive for 

 exploration. The greater area of the Carson Desert and the difficulty of securing 

 accurate information from surface studies as to the probable structure of this basin 

 would render a search for salines almost as difficult as in the Black Rock Desert. 



The U. S. Geological Survey put down a bore in the Carson Desert at what was 

 hypothetically assumed to be the axis of the deepest depression in the Quaternary 

 lake basin. The site of the bore is close to the north end of Timber Lake in sec. 

 30, T. 21 N., R. 30 E. The bore was sunk to a depth of about 985 feet and failed to 

 penetrate either saline beds or brines. The log of the bore to a depth of 320 feet is 



lltli|i|f|i|iMf i iiifi'i|ffli|ff^^ 



Fig. 8.— Cross sections showing probable conditions existing in Carson Lalse at different stages of 



desiccation. 



published in the bulletin noted below. ^ Sand, clay, and quicksand were the prin- 

 cipal sediments penetrated to this depth. Artesian water was encountered at a num- 

 ber of different levels. Examination of these waters showed them to be of low saline 

 content. Certain samples showed from 0.10 to 0.22 per cent potassium. ^ Other water 

 samples showed from traces to 0.1 per cent. At greater depths than that established 

 by the record it is said that no notable quantity of saline material was found. A 

 study of the Carson topographic sheet, together with the information shown by this 

 bore, indicates that the bore was put down in the delta material deposited by the 

 Carson River. That this delta deposit is of great thickness and outside of the area of 

 possible occurrence of saline beds is not an unwarranted conclusion. We would 

 expect sedimentation to be most active at the mouth of the Carson. Examination 

 of older and more recent maps indicates changes in the position of the Carson River 

 where it enters Carson Lake. The delta formed by the Carson during the Quaternary 

 lake period must have been eroded in part and must have supplied the alluvial mate- 

 rial of the present delta. The probable changes which took place during the evapora- 

 tion of Carson Lake in this delta material and in the deeper portions of the basin are 

 represented by figure 8. Three stages are indicated. In the first stage, or the begin- 

 ning of desiccation, a deep lake is represented, in one end of which is a considerable 

 delta deposit. The finer sediments and silts carried into the lake are represented 

 as a thicK bed upon the bottom. As the lake evaporated, erosion began in the former 

 delta deposit and a new delta began to form from the debris of the old. This new 

 delta would be expected to reach out as the lake evaporated and, as it were, push 

 the lake farther and farther down its bed. The end of the desiccation period is 

 represented in the h sketch. On the resumption of greater rainfall we would expect 

 silts and sediments to be brought down from the erosion of the remnants of the older 

 delta. Under certain conditions the saline beds would be closed over by this mate- 

 rial. The bottom diagram, figure 8, shows the conditions at the end of the third period. 

 An examination of c section would indicate that the saline deposits would be removed 

 at some considerable distance from the remnants of the old delta. The flatness of the 

 Carson Desert and its extent, particularly to the east, needs to be seen to be appreciated. 



iBul. No. 530A, U. S. Geo!. Survey, p. 18. 



2 Probably on to^al soli 's. 



