instructions from the war department. 11 



Office Pacific Railroad Surveys, 



Washington, May 1, 1855. 

 Sir : By direction of the Secretary of War, you will report to Lieut. R. S. Williamson, Topo- 

 graphical Engineers, for duty on the explorations and surveys in California and Oregon, with 

 which he is charged. 



It is understood that you are second in rank of the party, and that, if sickness or any acci- 

 dent should disable Lieut. Williamson, so as to oblige him to relinquish the command, you 

 will succeed to the charge and command of the party. 

 Very respectfully, your obedient servant, 



A. A. HUMPHREYS, 

 Captain Corps Top. Engineers, 



In charge of office for Pacific Railroad Surveys. 

 Lieut. Henry L. Abbot, 



Corps Topographical Engineers. 



SYSTEM ADOPTED IN PREPARING THE REPORT. 



In preparing the report of the explorations and surveys, made in accordance with the above 

 orders, I have adopted the following system : Part I contains the- general report, divided into 

 seven chapters ; of which the first contains a general description of the different regions traversed 

 during the survey. This synopsis has been prepared partly to enable those wishing merely to 

 obtain a general idea of the country, to dispense with reading a mass of details, and partly to 

 render the railroad report more intelligible. The second chapter is devoted entirely to a 

 discussion of the facilities offered for the construction of a railroad near the lines of survey. 

 The third, fourth, and fifth chapters contain a narrative and itinerary of the exjiedition. An 

 attempt has been made to give, in this portion of the report, a detailed description of the nature 

 of the country examined ; of the supply of wood, water, and grass near the trails ; of the character 

 of the Indian tribes ; and of various other matters, interesting to those who wish to thoroughly 

 understand the character of the regions explored. The sixth chapter contains a statement of 

 the method used in computing altitudes from observations taken with the barometer. The 

 seventh chapter contains an account of a former exploration of Lieut. Williamson, near a portion 

 of our line of survey. 



Parts II, III, and IV, contain geological, botanical, and zoological reports upon the regions 

 explored. 



The various appendices exhibit, in a tabular form, the astronomical and barometric observa- 

 tions, with the results deduced from them by computation. 



MAPS ACCOMPANYING THE REPORT. 



Two maps, constructed upon the polyconic projection, have been made to accompany this 

 report. The first illustrates that portion of the survey which lay in California, and the second 

 that in Oregon. The scale of each is one inch to twelve miles, or 1:760320. 



The data, upon which these maps have been constructed, will be briefly stated. The distances 



