106 THE DESICCATION OF LATER GEOLOGICAL TIMES. 



During the progress of the California Geological Survey the evidences of 

 the diminution of the water in the lakes on the eastern slope of the Sierra 

 Nevada Avas a matter of frequent observation and comment. The terraces 

 around the shores of Mono Lake proving its former much greater depth and 

 larger area were described in the Geology of California, Vol. I.* (1865). The 

 highest terrace is there mentioned as being at an elevation of 680 feet above 

 the present level of the lake. The possible connection of Mono with Walker's 

 Lake, in past ages, is suggested, and the probable connection of these an- 

 cient greatly expanded lake-areas with the phenomena of extinct glaciation 

 insisted upon. The subject was brought up again in the Yosemite Guide- 

 Bookt(18G9) in the following words: "That there was formerly a much 

 greater precipitation of moisture on the eastern side of the Sierra than there 

 now is, seems proved by the former greater extension of the lakes on the 

 eastern slope. Mono Lake, for instance, is surrounded by terraces or benches, 

 which show that its surfiice once stood 600 feet higher than it now does, and 

 the same is true of Walker, Pyramid, and the other lakes on that side of the 

 Sien-a. No doubt at that time the now arid valleys of Nevada were beau- 

 tiful inland seas, which filled the spaces between the lofty parallel ridges by 

 which that State is traversed. Perhaps the slopes of those ridges were then 

 clothed with dense forests, offering a wonderful contrast to the present bar- 

 renness of the ranges, and the monotony and desolation of the alkaline 

 plains at their base." 



The somewhat elaborate and very costly surveys and explorations carried 

 on, since the stoppage of the California State Geological Survey, in the region 

 of the Cordilleras, under authority of the United States, have developed a 

 large bod}^ of facts additional to, and corroborative of, what had been pre- 

 viously stated by the present writer in respect to the great diminution in 

 the area of the lakes of the Great Basin and of the Cordilleras in general. 

 Mr. G. K. Gilbert seems to have been the first person to go into any detailed 

 description of the phenomena in question, and his remarks will be found in 

 the volume of Geology publislied by the Wheeler Survej'.t 



Mr. Gilbert adds his testimony to that previously accumulated in reference 

 to the absence of any proofs of a movement of the detrital materials on the 



* Geology of California, Vol. I. p. 451. 



t The Yosemite Guide-Book : A Description of the Yosemite Valley and the Adjacent Region of tlie Sierra 

 Nevada, and of the Big Trees of California. An official puhlieation of the Geological Survey. 



t See Report upon Geographical and Geological Kxploratious and Surveys West of the One Hundredth lleriJiau, 

 ill charge of First Lieut. Geo. M. Wheeler, Vol. 111., Geology. Washington, 1875. 



