National Geographic : 1900 Jan
24 THE IDAHO AND MONTANA BOUNDARY LINE (see illustration, page 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 appropriation, as the available funds were exhausted on the part of the line first mentioned. From a geological standpoint, but hardly from a practical one, however, there is another reason why 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 slowly 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 representing the original divide, if the latter may be accepted as having passed through the highest points of the range, which seems probable. Points near the meridian line were located by triangulation from the Spokane base of the U. S. Geological Survey, this base being referred for its initial latitude and longitude to two astronomic piers in the court-house grounds at Spokane, the latitude determination having been made by the U. S. Geological Survey and the longitude deter mination by the U. S. Coast and Geodetic Survey. After the point on the crest of the Bitter Root Mountains corre sponding to its intersection with the 39th meridian had been located, this location having been determined by 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 establish a triangulation station near the line at its intersection with the inter national boundary, so from the most northerly location by triangu * There has been considerable discussion as to just what constitutes the Bitter Root Range. The law defining the boundary line between Idaho and Montana implies that the range extends at least from Lake Pend d'Oreille 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 Cceur d'Alene Mountains, extend ing from the vicinity of Lake Pend d'Oreille to St Regis Pass; the St Regis Mountains, ex tending 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 Divide.