LETTER TO THE SECEETARY OF WAR. 



WASHINGTON, D. C., May 6, 1857. 



SIR : In obedience to instructions from the War Department, I have the honor to submit the 

 accompanying report of the exploration and survey in California and Oregon, conducted by 

 Lieutenant R. S. Williamson, United States Topographical Engineers, in 1855. The prepara 

 tion of the report has devolved upon me, in consequence of the severe and protracted illness of 

 Lieutenant Williamson ; and it is due to myself to state that I have performed the duty with 

 extreme reluctance, partly because it was not originally designed for me by the Department, 

 and partly because it properly belongs to the officer by whose forethought and professional 

 ability the expedition has been brought to a successful termination. 



Wishing to convey Lieutenant Williamson s ideas, as far as they are known to me, I have 

 been guided by his recorded field notes, and by his opinions expressed to me in conversation, in 

 preparing the portion of the report which relates to regions traversed by him. During a part 

 of the field work I was entrusted with a separate party, with instructions to prepare a written 

 report of the results of my examinations. For any opinion given in this portion of the report 

 he, of course, is not responsible. 



At the completion of the survey for a railroad route from the Sacramento valley to the Columbia 

 river, the season was so far advanced and the animals were in so jaded condition, that Lieutenant 

 Williamson considered it impracticable to make any examination of the Sierra Nevada until the 

 ensuing spring. Before that time, orders were received from the War Department, directing 

 him to return at once to Washington to prepare the maps, profiles, and reports of the explora 

 tion already made. The second survey contemplated in his original instructions was consequently 

 omitted. 



At Lieutenant Williamson s request, I have prepared a full statement of the method used in 

 deducing altitudes from the barometric observations. For unpublished and very valuable inform 

 ation on this subject, I am indebted to Captain A. W. Whipple, United States Topographical 

 Engineers. 



I should do injustice to Lieutenant Williamson, if I did not express his high appreciation of 

 the energy and ability with which the officers of the escort, and the civilian assistants, labored 

 to advance the objects of the exploration. 



Of those who accompanied me when detached from the main command, I feel at liberty to speak 

 in less general terms. Lieutenant Crook, who was the only officer with me, officially and 

 personally contributed, in a high degree, to the success and to the harmony of the expedition. 

 Mr. Fillebrown and Mr. Young, although suffering from severe attacks of intermittent fever, and 

 deprived of the services of a physician, willingly continued with the party, and discharged their 

 accustomed duties with energy and accuracy. The masterly sketches of views upon the route, and 

 the characteristic style of the topography upon the accompanying maps, testify to the professional 

 skill of Mr. Young. Mr. Anderson, who was my only scientific assistant in some of the most 

 difficult and perplexing portions of the survey, aided me in every way in his power. To him, 

 and to Mr. Fillebrown, the government is chiefly indebted for the numerous barometric observa- 



