LETTER TO THE SECRETARY 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 tlio 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 For unpublished and very valuable inform¬ 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- 
