REPORT OF HENRY GANNETT, M. E. 



CHAPTER I. 



METHODS OF WORK. 



The area assigned to the Green Biver division for survey during the 

 season of 1877 was approximately a rectangle, limited in longitude by 

 the meridians of 109° 30' and 112° 00', and in latitude by the parallels of 

 41° 45' and 43° 00', embracing parts of Wyoming, Idaho, and Utah. The 

 area of this " rectangle " is about 11,000 square miles. This district was 

 surveyed, and then, the season not being ended, the work was continued 

 westward to the meridian of 112° 30', making the total area surveyed 

 during the season about 13,000 square miles. One hundred and forty- 

 seven stations were made with the gradienter, besides about two hun- 

 dred minor stations and locations. The number of horizontal angles 

 measured was 9,200 ; of vertical angles (for relative height), 1,960. 



METHODS OF SURVEY. 



As a basis for the secondary triangulation and topographical work, 

 twelve points, fairly distributed, were established by the primary trian- 

 gulation within or near the district assigned me. The secondary trian- 

 gulation was carried on by myself in connection with the topographical 

 work, the instrument used being the " gradienter," a compact, strong, 

 theodolite, reading, to minutes. With this instrument twenty-two sec- 

 ondary stations were located by closed triangles, while the other sta- 

 tions were established by incomplete triangles and the " three-point 

 problem." 



To illustrate the character of the secondary triangulation, the follow- 

 ing triangles, with their summing up, are presented. The asterisk after 

 the name of a station indicates a primary station. 



Angle. 



Soda Peak* 25Q13' 



Station 108 '. .. 19 14 



Paris Peak* 135 35 



180 02 



Soda Peak* 100 30 



Paris Peak* !,... 41 28 



Snow Mountain 38 08 



180 06 



a Station 79 is the point established by this triangle. 



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