ie ا‎ ys 
LETTER TO CAPTAIN A. A. HUMPHREYS, TOPOGRAPHICAL ENGINEERS. 
War DEPARTMENT, OFFICE or EXPLORATIONS AND SURVEYS, 
Washington, D. C., March 1, 1858. 
Sir: In D the **map of the territory of the United States from the Mississippi river 
to the Pacific ocean, ordered by the Hon. Jefferson Davis, Secretary of War, to accompany the 
reports of the explorations for a railroad route," my instructions were to carefully read every 
report and examine every map of survey, reconnaissance, and travel which could be obtained, 
to ascertain their several values, and to embody the authentic information in the map. This 
duty is now to the best of my ability completed. 
The maps used in the compilation have been mostly made from reconnaissances, and but few 
possess very great accuracy. The geographical positions are therefore rarely determined 
absolutely, or even relatively, with certainty, and new surveys are constantly making slight 
changes necessary. The work of compilation, therefore, must necessarily be frequently 
repeated; and to aid the future compiler, I have prepared the accompanying memoir upon 
. the different maps and books used, and upon the manner in which their discrepancies -have 
been reconciled. 
This memoir is a brief account of the numerous explorations made in our territory west of 
the Mississippi river, and I hope may prove valuable to those seeking information with a view 
to developing the resources of this vast region, as well as interesting to those studying the 
progress of geographical discovery. The work has been in progress during the past four 
years; but other public duties have absorbed the greater part of my time, which must be my 
excuse for its defects. For the beautiful execution of the topography upon the map, I am 
mainly indebted to Mr. E. Freyhold and Mr. F. W. Egloffstein. 
I have the honor to be, very respectfully, your obedient servant, 
G. K. WARREN, 
First Lieutenant, Topographical Engineers. 
Captain A. k HUMPHREYS, 
Corps of Topographical Engineers, in charge of Office of Explorations and Surveys. 
