When Congress established a new territory of Montana, May 26, 1864, from what then was northeast Idaho, the present Idaho-Montana boundary was fixed by statute. The line Congress chose was mainly the Bitterroot range and, farther south, the Continental Divide. The boundary seemed entirely satisfactory to the Montana people who suggested it and prevailed upon Congress to divide Idaho and make their land into a new territory. Objections were raised in Idaho, but they were entirely too late. No one in Idaho, in fact, found out about the proposed Montana boundary in time to try to get it changed before President Lincoln signed the act into law.
A great many years after the Bitterroot boundary had been defined by law, a decidedly peculiar legend grew up. In this strange legend the choice of the Bitterroots, instead of the Continental Divide, is blamed off on a misguided boundary survey part. More than one variation of this fictitious account of the boundary choice is available: the surveyors got drunk and did not know what they were doing, or were bribed by unscrupulous Montana agents, or got too excited about gold mining to pay attention to their job, or had defective equipment, or simply got lost and followed the wrong range of mountains. In any event, the legend has it that the boundary surveyors made a truly colossal error in following the Bitterroots instead of the Continental Divide as they allegedly were supposed to--and that as a result Idaho lost Missoula, Butte, and all the rest of Montana which is west of the Rockies.
In actual fact, surveyors in the field (whether lost, drunk, or even sober) had nothing whatever to do with the selection of the Bitterroot range for the boundary. The Idaho-Montana line was fixed clearly and definitely where it now is (and always has been) by act of Congress of May 26, 1864. The actual survey and demarcation of the line along the Continental Divide (a total of 312 miles) and Bitterroots (a total of 355 miles) was not even undertaken until 1904-1906. (How Idaho and Montana got along with no boundary at all until after 1904 is an interesting subject that the legends neglects.) When the boundary actually was marked, moreover, the surveyors started at the north and proceeded south along the Bitterroots to the Continental Divide, rather than the other way around, as the legend has it. Going the way they did, from north to south, they could not possibly have mistaken the Bitterroots for the Continental Divide where the two ranges come together north of Salmon; they already were coming south along the Bitterroot range before they reached the Continental Divide. The legend of the lost surveyors of the Idaho-Montana boundary thus lacks even the slightest hint of factual truth. Idaho and Montana got along for forty years without bothering to have the mountain part of their boundary surveyed, and although the merit--or lack of merit--of the line along the Bitterroots sometimes was discussed, the argument had nothing whatever to do with boundary surveyors, or with the undisputed fact that the boundary was there.