66 BULLETIN 61, U. S. DEPARTMENT OF AGRICULTURE. 
F. L. Hess 1 describes the occurrence of gypsum in recent lake beds in theMojave 
Desert, Cal. The beds occur in a periodic lake in the vicinity of Amboy, Cal. Bristol 
Lake is the name given to the area. The gypsum occurs in the lake bottom close to 
the shores of the lake. The bed is of variable thickness and its maximum thickness 
has not been determined. In one place gypsum was found to a depth of 9.5 feet, the 
upper layers being more or less mixed with dirt. A brine is reached in the lake bed 
at a depth varying from 8 to 10 feet. Prospect holes show the deposit to be confined 
from within one-half to 1 mile of the old shore line. The gypsum is of a granular nature. 
Hess ascribes the localization of a deposit of this kind as being due to the greater 
evaporation rate of the lake waters near the shore. Capillarity in the marginal material 
also undoubtedly has contributed to the local concentration of the gypsum. 
Rock gypsum is being mined at Mound House, Arden, and Ludwig. The deposits 
are of considerable commercial importance. The gypsite deposits at Mound House 
were worked for a time, but have been idle for some years. They are of doubtful 
value. The gypsum at Bristol Lake is reported by Hess as being exploited by the 
Pacific Cement Plaster Co. 
CONCLUSION. 
Repeated reference has been made to the Stassfurt deposits of Germany in connec- 
tion with the search for potash salts in the United States. While this has served a 
useful purpose in stimulating the search for salines, it perhaps has resulted in the 
opinion that similar deposits might be expected in the Great Basin. Such a view 
can not now be held. The German deposits are in the Triassic and they, as well as 
the associated sedimentaries, have been folded and tilted. They represent complete 
desiccation and more or less secondary action before, during, and after tectonic dis- 
turbance. Omitting from present consideration the deposits of the Jurassic and 
Tertiary, the saliniferous deposits of the Great Basin may be said to represent com- 
paratively recent geologic activity. They are confined to the Quaternary lake and 
desert basins. The older deposits were formed in earlier periods of desiccation, but 
desiccation did not reach extreme conditions. The present deposits are in process 
of formation. Very little disturbance of the Quaternary and recent sedimentaries has 
taken place. More or less secondary action, such as solution, re crystallization, and 
movement of brines, is taking place. It may be said that the basin deposits already 
discovered represent the initial stages of what in time might result in deposits rather 
remotely similar to Stassfurt, but of much less magnitude. 
The influence of regional rocks has been commented upon and the prevalence of 
volcanics in the Great Basin has caused geologists to turn to this region as a place in 
which to look for potassium salts. Regional differences, caused by the prevalence 
of different types of rocks, are manifest in the presence of alkali carbonates and 
borates in the western part of the Great Basin and the presence of chlorides in the 
eastern portion where sedimentaries predominate. In the case of potassium, no 
such marked difference is shown. The potassium content in the saline residue of the 
water of Great Salt Lake is not much less than that of Mono, Owens, and Pyramid 
Lakes. Humboldt Lake, North, Middle and South Alkali Lakes, it is true, show a 
higher content of potassium, but these are relatively unimportant. The resistance 
to weathering of the potash-rich minerals and the ease with which this element is 
absorbed and removed from surface and underground waters might well account for 
the low content of potash in all of the lakes. 
With the exception of the crusts and efflorescences about hot springs and in soils, 
no notably high potassium content has been reported from salines taken from beds. 
The potassium content in material of this nature ranges from less than 1 to 2 per cent. 
It is not in the salts which have crystallized out, but in the residual brines or mother 
liquors that concentration of potassium has taken place, and it is to these that we 
must look for potassium salts. As desiccation approaches completion, so will the 
residual brines increase in proportion of potassium. A near approach to complete 
desiccation would give a brine high in potash. The fortuitous absorption and sealing 
oyer of such a brine would protect it from further changes, except those produced by 
circulating underground waters. It is evident that the above action might occur at 
different stages of desiccation, and brines varying in degree of potash content would 
be absorbed and sealed in the same way. Sealing would not necessarily have to be 
caused by the formation of impervious layers, although this would be more effective 
than a layer of sand. A layer of sand, subsequently flooded with water, would deplete 
by diffusion the partially concentrated brine beneath and, in time, a much weaker 
brine would result. It should be noted that the abi orption of saline waters which 
» Bui. No. 413, U. S. Geo]. Survey, p. 125. 
