40 BULLETIN 54^ U. S. DEPAETMENT OF AGRICULTURE. 



At its northern end Owens Valley now receives the drainage of Long Valley, and 

 doubtless once received that of Adobe Valley, now a region of several local depressions. 

 Except for the loss of Adobe Valley the basin has suffered very little by stream decay, 

 ha-\'ing been saved by its proximity to the Sierra. The present area of the Owens 

 Basin ia 2,550 square miles; with the Adobe Valley it is 2,825 square miles. 



THE SEARLES BASIN. 



The Searles Basin lies directly south of the Owens, and the greater portion of its area 

 is a direct continuation of the Owens Valley trough. The deepest depression, how- 

 ever, lies eastward beyond the Argus Range, which is here ciit by a narrow canyon 

 of erosion — Salt Wells Canyon. This deepest depression is the so-called Searles Lake. 

 The triljutary area to the west is known in various parts as the Indian Wells, China 

 liake, and Salt Wells Valleys. The bottom of the Searles depression is a body of white 

 crystalline salts almost 12 square miles in area and with a maximum depth of about 

 75 feet. (PI. V, fig. 1.) Under this are saline muds and sands, sometimes more or 

 less cemented. The salts are mainly the chloride, carbonate, and sulphate of sodium, 

 with lesser amounts of borax and of salts of potassiimi, the latter being largely in the 

 brine which saturates the salt body. The potassium and other salts are believed to 

 be very valuable commercially, and preparations are now under way for their 

 exploitation. 



The Salt Wells Canyon is pre-Lahontan, but the lake which occupied Searles during 

 the Lahontan period stood a little over 600 feet above the present salt fiat and extended 

 through this canyon and a considerable way into the valley to the west. Both then 

 and since this latter valley has acted as a^settling basin for alluvium, and this is believed 

 to have much to do with the exceptional purity of the Searles salt body. A series of 

 old lake and estuarine beds clinging to the walls of Salt Wells Canyon records a period 

 of some length during which the lake stood at a moderate elevation, perhaps 300 feet 

 above the present surface, and permitted the partial filling of the canyon, which was 

 then an estuary. This same intermediate level and several others, both above and 

 below it, are recorded in a complex beries of lake terraces, tufa deposits, etc., which 

 surround the basin. (PI. V, fig. 2.) These relicta of the ancient lake have suffered 

 much more by erosion than have the similar records of Lakes Lahontan and Bonne- 

 ville, but the significance of this fact is yet obscure. 



It will be recalled that the Owens Valley probably once overflowed into Searles 

 through the Salt Wells Valley, and it is quite possible that Searles itself had a period 

 of overflow. The highest of the lake strands about the bashi is a trifle over 600 feet 

 above the floor and the divide at the southern end of the basin between it and the 

 drainage of the Panamint is at very nearly the same elevation. It is possible that 

 the lake spilled for a time over this divide into the Panamint. The question could 

 doubtless be settled by a careful study of tHs divide and the approaches to it, but 

 the study has not been made, and it is not now possible to be certain. In any case, 

 the lake can hardly have overflowed for long, since the divide is not an alluvial dam, 

 and, if anything, has probably been lowered rather than raised by post-Lahontan rain- 

 wash. Furthermore, the series of terraces below the divide indicates a long and 

 varied independent existence of the lake, and the absence of tufa on or near the highest 

 terrace suggests that when the lake did overflow (if it did) it was essentially fresh. 



At the present time the tributary valley west of Searles has suffered greatly by 

 stream decay and has come to contain a large number of more or less local playas, the 

 most important of which is China Lake. All these are shallow and recent and 

 W(juld again become tributary to Searles if the rainfall wore to increase only very 

 slightly. Including them and the whole of its present tributaries the area of the 

 basin is 2,030 square miles. With the entire Owens Baain the area is 4,850 square 

 miles, which almost certainly represents its area during the Lahontan period. 



