12 SURVEY OF IDAHO-MONTANA BOUNDARY LINE. [bull.170. 
certified to by the Director of the Geological Survey, and three copies thereof shall 
be returned, one for filing in the surveyor-general's office of Idaho, one in the 
surveyor-general's office of Montana, and the original in the General Land Office. 
In carrying out the provisions of the law above quoted three special processes 
are involved: 
First. The accurate location of the thirty-ninth meridian on the ground by tri- 
angulation from the Spokane base of the United States Geological Survey, includ- 
ing the retracing of so much of the international boundary line as may be found 
necessary for the determination of the intersection of the thirty-ninth meridian 
with the said boundary line, as well as for locating points on the continuation of 
the boundary between Montana and Idaho along the summit of the Bitterroot 
Mountains. 
Second. The marking on the surface of the ground, by proper monuments, of 
the boundary as determined. 
Third. The preparation of the necessary plats and field notes. 
With reference to the above, the following instructions will be observed: 
LOCATING THE BOUNDARY. 
The Spokane base of the United States Geological Survey is referred to the 
meridian of Greenwich, and the thirty-ninth meridian above mentioned has for 
its initial point the meridian of the old Naval Observatory at Washington. By 
applying the proper correction and referring the thirty-ninth meridian west of 
Washington to the meridian of Greenwich, the result is that the meridian to be 
determined as the boundary line between Idaho and Montana is 116° 03' 02". 30 
west of Greenwich. 
The tri angulation from the Spokane base will be extended eastward so as to accu- 
rately locate the intersection of the meridian above mentioned west from Green- 
wich with the summit of the Bitterroot Mountains. It may be that this identical 
point can not be located directly by triangulation, but a point as near thereto as 
may be possible should be so located, and from this the exact point should be 
determined by careful traverse based on an astronomic or calculated azimuth 
and distances determined by direct chaining or stadia measurement, whichever 
may be most practicable. 
After the point referred to, namely, tli6 intersection of the meridian 116° 03' 02". 30 
west from Greenwich with the summit of the Bitterroot Mountains, has been 
determined, the triangulation is to be extended northward, locating as many 
points as may be practicable as near as may be to the boundary line between 
Idaho and Montana until the international boundary is reached. From the points 
so located by triangulation other points exactly on the boundary will be deter- 
mined by traverse in the manner hitherto mentioned. The international bound- 
ary line is supposedly on the forty-ninth parallel of latitude. It will not, however, 
answer the purpose to rely on the location of this parallel from the Spokane base, 
but it must be determined with reference to an existing monument or monuments, 
being carefully retraced until its point of intersection with the meridian is exactly 
located. 
The distance along the international boundary from the nearest monument, or 
the monument recovered, to the point of intersection will be determined either by 
triangulation or direct measurement with chain or stadia or a combination of the 
two methods. 
After points as above described have been located on the boundary line between 
Idaho and Montana from the international boundary to the summit of the Bitter- 
root Mountains, these points will be joined by true meridian lines, so that a suffi- 
cient number of points on the boundary in addition may be determined to fulfill the 
conditions made necessary under the provisions hereinafter mentioned for mark- 
