24 THE IDAHO AM' MOXTAXA BOl'SDAItY LIXK 



(see illustration, i)age 26), it was not considered necessary to place 

 monuments along this portion of the line, nor would it have been pos- 

 sible to do so under the a))propriation, as tiie available funds were 

 exliausted on the part of tlie line first mentioned. F'rom a geological 

 standpoint, l)Ut hardly from a practical one, however, there is another 

 reason wh}- monuments should not be placed on the summit of the 

 Bitter Root Range* as marking the boundary line between Idaho and 

 Montana. There is abundant evidence that the summit is what is 

 known as a retreating or migrating divide ; in other words, the waters 

 tributary to the Bitter Root River in Montana are continually capturing 

 by erosion those of the Clearwater River in Idaho, so that the divide is 

 slowl}' being shifted to the westward, thus adding to the territory' of 

 Montana and diminishing that of Idaho. The existing divide is uni- 

 formly from six to eight miles from the irregular line rejiresenting the 

 original divide, if the latter may be accepted as having passed tlirough 

 the highest points of the range, which seems probable. 



Points near the meridian line were located l)y triangulation from the 

 S{)okane base of the U. S. Geological Survey, this base being referred 

 for its initial latitude and longitude to two astronomic jiiers in the 

 court-house grounds at Spokane, the latitude determination having 

 been made by the U. S. Geological Surve}' and the longitude deter- 

 mination by the U. S. Coast and Geodetic Survey. 



After the ])oint on the crest of the Bitter Root Mountains corre- 

 sponding to its intersection with the 30th meridian had been located, 

 this location having been determined 1)}^ traverse from the triangula- 

 tion station divide (see diagram of triangulation on page 25 ), a random 

 line was run northward to the international boundary by transit and 

 stadia, horizontal and vertical distances being measured. Direction 

 was controlled by frequent observations for azimuth. The line was 

 further checked in azimuth, as well as in distance, by connection with 

 the triangulation at four points. It was not practicable to estal)lish 

 a triangulation station near the line at its intersection with the inter- 

 national boundary, so from the most northerl}^ location b}' triangu- 



* There h,is been eonsirlerable discussion as to just what constitutes the Bitter Root Range. 

 Tlie law defining the boundary line between Idaho and Jlontana implies that tlie range e.xtends 

 at lea.st from Lake Pend dOreille to the Continental Divide, and it seems to the writer, as well 

 as to others interested, that this designation should stand. There are, however, topographic and 

 geologic considerations which make it desirable to differentiate somewhat, and it is proposed 

 that the Bitter Root Range be subdesignated as follows : The Cojurd'Alfene Mountains, extend- 

 ing from the vicinity of Lake Pend d'Oreille to St Regis Pass; the St Regis .Mountains, ex- 

 ending from St Regis Pass to Lolo Pass; the Lolo Mountains, extending from Lolo Pass to 

 Nez Perces Pass, and the Nez Perces Mountains, extending from Nez Perces Pass to the Con- 

 tinental l>ivide. 



