di 
GRADUAL DESSICATION OF THE VALLEY. 193 
found to consist of carbonate of soda, sulphate of soda, sulphates of lime and magnesia, in traces, 
and chloride of sodium or common salt. (See specimen No. 256 of the collection.) 
The two lakes—Buena Vista and Kern—are at the southern extremity of the valley ; they 
are visible from the ridges of the Tejon Pass and the Cañada de las Uvas. They are compara- 
tively small in extent, but their area is not known. Their positions have been well determined 
by the Survey, and they are, for the first time, correctly laid down upon a map.! 
There does not appear to be much vegetation about these small lakes ; itis probable that they 
are liable to great changes of area, so great, that the conditions of moisture are not favorable to 
organic growth. Kern Lake was found, by barometrical observation, to be at an elevation ot 
398 feet above the sea. 
Evidences of a former submergence of the Valley.—From the facts that have been stated in 
regard to this valley, it becomes evident that at a former period the lakes were more extensive ; 
and that, in fact, the greater part of the valley was submerged by a broad lake. 
The broad, alluvial tracts of clay soil along King’s River and the Four Creeks, and the exten- 
sive plains of similar alluvial character, far from any water-courses, and above the reach of 
modern inundations, may be regarded as having a lacustrine origin. The limits of this alluvial 
formation may be considered as marking the former area or extension of the lake. I have taken 
the observations made at distant points, and from them drawn the limits of the alluvium on the 
Geological Map, and colored it to cortes with the alluvium of the delta of the Sacramento 
and San Joaquin. 
All the facts indicate that this wide area was formerly covered with fresh water, and that it 
` has been gradually drying up. Although there may have been extraordinary floods, at intervals, 
which caused the lakes to extend nearly to their ancient limits, the prevailing tendency has 
been to a complete dessication of the region. 
It is not easy to give a definite and precise explanation of the cause of this gradual dessica- 
tion. It is probable that it is partly due to a change of level, whereby the valley was drained. 
It is also probable that depositions of sediment by the San Joaquin, and other streams, have 
raised the level of that end of the valley near the San Joaquin, so as to shut off the communica- 
tion with this river. It is very possible that the principal part of its water was formerly 
delivered to the lakes. 
Rapidity of evaporation from the surface of the lakes.— Whatever cause may be assigned for 
the change in the condition of this valley, the rapidity of evaporation from the surface of the 
water in that region should not be overlooked in the attempt to solve the problem. The amount 
of water that is taken up by the winds in that valley is astonishing. We have seen that during 
the dry season the lakes have no outlet, and that they are constantly receiving great quantities 
of water from the rivers; the evaporation from their surfaces must then be equal to, if not 
greater than, the supply. The conditions under which these lakes are situated could scarcely 
be more favorable for this result. The strong winds that rush inland from the Pacific during 
the day, pass over the broad, heated plains, and the numerous ranges of the Coast M u tair 
before they reach the valley. They thus part with the greater portion of their moi before 
e pour in upon at Tulares. The shores of the ies Deine, pa and shelving, and without 
no racio £r. TW these Be US Sem. | they : E a1. jr A and absorb 
f : HUS y 
the water with nd rapidity. The rapidity cad the 'vaporat tion. is increased by the tem- 
pie un alo, theaco SEE g Ge a aso | a 3 
25 ۳ 
77۳۳9 
