20 GEOLOGICAL niSTOIlY OF LAKE LAHONTAK. 



iciilly surveyed. l^'roiii the exiurieiire gained during the first season's 

 \v())k, a |ilaii of investigation was developed which was carried oiit during 

 the suunners i>f 1S,S2 and 1883. 



On taking- the field at Winneniucca, Nevada, in the spring- of 1882, 1 

 was joined hy Mr. Willard D. Johnson, of Washington, 1). C, who accom- 

 panied nie on a journey tln'ough that j)ortion of the Great Basin that Hes 

 north of the hydrographic rim of Lake Lahontan and is situated mostly in 

 Oregon. The results of this exploration, so far as the surface geology of 

 the region is concerned, were published in the Fourth Annual Report of the 

 United States Geological survey. During this reconnaissance the pre- 

 vious conclusion that liake Lahontan did not overflow northward was fully 

 confirmed. The Great Basin noi'th of the Nevada-Oregon boundary, in 

 connnon with the main area of interiin- drainage, is divided into a number 

 of independent hydrographic basins, many of which held Quaternary lakes 

 that must have been contemporaneous with the great lakes of Utah and 

 Nevada 



On returning to Winnemucca in July, I was johied by Mr. W J McGee 

 as geological aid, and a few weeks later by Mr. George M. Wright, also in 

 the same capacity. Proceeding southward from Winnemucca we examined 

 the Lahontan sediments, terraces, tufa deposits, etc., occurring in the Hum- 

 boldt Valley, and then contiiuied our journey southward in order to study 

 the region about Humbolt, Pyramid, Winnemucca, and Walker lakes. 

 Later in the season we entered the Mono Lake basin and began a detailed 

 investigation of its Quaternary geology. Owing to the advance of winter 

 we were obliged to leave the completion of this work until another season. 



During the time that the expeditions mentioned above Avere being car- 

 ried forward, ]\h'. A. L. Webster, assisted by Mr. Eugene Ricks6cker, was 

 engaged in making a topographical survey of the northeast portion of the 

 Lahontan basin, in order to complete the compilation of the accompany 

 ing pocket map. The region surveyed by Mr. Webster embraced about 

 8,464 square miles, and is indicated on Plate II ; the extreme eastern limit 

 of the area surveyed is a few miles to the eastward of the right-hand bor- 

 der of the plate. 



