PREFACE. 



In the year 1874 my kind friend Prof. J. W. Powell proposed to me 

 that I should undertake, under his direction, the study of a large volcanic 

 tract in the Territory of Utah, provided the consent of proper authority 

 could be entertained. Distrusting my own fitness for the work, I felt that 

 it would be better for him if his proposals were thankfully declined. In 



1875, however, he renewed the proposition in such a friendly and compli- 

 mentary manner that a refusal seemed ungracious. He therefore laid the 

 matter before the Secretary of War, the General of the Army, and the 

 Chief of Ordnance, all of whom gave their cordial approbation; and by 

 order of the War Department I was detailed for duty in connection with 

 the survey of the Rocky Mountain Region in charge of Professor Powell. 

 The field which he assigned me to study was the District of the High 

 Plateaus, and the investigations were made during the summers of 1875, 



1876, and 1877. The preparation of a report or monograph upon the dis- 

 trict has several times been interrupted by the pressure of other official 

 duties to which the writer has been assigned during the last three years. 



In submitting this work, the dominant feeling in my ov,"n mind is a 

 keen sense of its many imperfections and a consciousness that it falls far 

 short of my hopes and expectations. The defects have arisen in a great 

 measure from want of experience in western geological field work prior to 

 the inception of this undertaking, and especially from want of observation 

 in the class of phenomena of which the work principally treats. Probably, 

 also, the magnitude of the task proposed was too great even for much more 

 experienced observers to accomplish within the time allotted to it. It 

 involved not only a study of the immediate district under discussion, but the 

 investigation of large areas surrounding it to which the district stands in 



