INSTRUCTIONS FROM THE WAR DEPARTMENT. 
11 
Office Pacific Railroad Surveys, 
Washington, May 1, 1855. 
Sir : By direction of tlie 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, 
Lieut. Henry L. Abbot, 
Corps Topographical Engineers. 
A. A. HUMPHREYS, 
Captain Corps Top. Engineers, 
In charge of office for Pacific Railroad Surveys. 
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 expedition. 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 
