18 GEOLOGICAL UISTORY OF LAKE LAHONTAN. 



way of Allen's Springs, and afterwards traversed Mason and Carson val- 

 leys, which, as we now know, were also oecnpied by the waters of Lake 

 Lahontan. The presence of ancient water lines and of calcareous tufa 

 deposits about the borders of the Carson Desert was recorded by Henry 

 Engelmann, the geologist of the expedition, in his report on the geology 

 of the country traversed during the reconnaissance, but time did not per- 

 mit an extended study of the surface geology of the region. That large 

 portions of the area of interior drainage had at no distant time been 

 occupied by lakes was clearly recognized, and the cause of their disappear- 

 ance was correctly ascribed to climatic changes. 



During the progress of the United States Geographical Surveys west 

 of the 100th Meridian, in charge of Capt. George M. Wheeler, large pov- 

 tions of the Lahontan basin were topographically surve37ed, but no report 

 on the geography or geology of the region has been published. The maps 

 prepared by this survey, and also those issued iu connection with the 

 exploration of the Fortieth Parallel, were exceedingly useful during the 

 field work of the present investigation, and were freely used in compiling 

 the jjocket map accompanying this report, as well as in preparing some of 

 the smaller illustrations. 



The exploration of the Fortieth Parallel included a belt 100 miles 

 wide which crossed the Lahontan basin, but left considerable areas both 

 to the north and south unmapped. Li the reports of that survey Lake 

 Lahontan received its name, and it is discussed to considerable length 

 by the geologist in charge (Vol. I). Many detailed observations relating 

 to the history of the former lake were recorded by Messrs. Arnold Hague 

 and S. F. Emmons as a part of their report (Vol. II) of field observations. 

 It is not necessary to introduce an abstract of the results reached by these 

 geologists in reference to the history of the former lake, as we shall have 

 frequent occasion to refer to their work in the pages that follow. 



In 1872 Dr. James Blake made a journey from Winneuuicca, Nevada, 

 to the Pueblo Mountains, Oregon, during which he traversed the northern 

 portion of the Lahontan basin, and made many observations in reference 

 to tufa deposits, terraces, fossil shells, etc. The results of these observa- 

 tions were [)nblished in two brief papers in Vol. IV (1872) of the Proceedings 



