PREFACE. 



The explorations reported in the present volume are a continuation of 

 the studies of the Quatei-nary geology of the Great Basin begun by Mr. 

 G. K. Gilbert when the present survey was organized. The work has been 

 carried out under Mr. Gilbert's direction, and to him I am indebted not only 

 for every facility he could offer for advancing my work, but also for im- 

 portant advice and numerous suggestions. Whatever value may be at- 

 tached to the results of my labors will be due in great measure to the 

 wisdom and unvarying kindness of the Chief of the Division of the Great 

 Basin. 



With the exception of the reconnaissance of 1881, I have had the 

 assistance of Mr. Willard D. Johnson in all matters relating to topography 

 throughout both the field and office work connected with the preparation of 

 this volume. The energy and completeness with which he has carried for- 

 ward his special work under peculiar difficulties, not met with outside the 

 desert regions of the Far West, deserve the highest praise The accuracy 

 of the accompanying maps that Mr. Johnson has drawn from his own sur- 

 vey will make them a reliable basis for determining future changes in the 

 lakes and rivers of the region explored. 



During the summer of 1882, I was accompanied by Messrs. W J Mc- 

 Gee and George M. Wright, as geological aids, and to each I have the 

 pleasure of crediting much valuable assistance. The accompanying draw- 

 ings of geological sections will attest the accuracy of Mr. McGee's work. 



The survey of nearly 8,500 square miles in nt)rthern Nevada, which 

 was necessary in order to coni])ile the accompanying pocket map and many 

 of the smaller illustrations, was carried out by Mr. A. L. Webster, assisted 



