Some of the earliest of these expeditions, after entering the unexplored region which afterwards became Idaho and Montana, were arrested by information that it would be impossible to cross, with teams, the several mountain ranges between them and the mines. This discouragement was followed up by intelligence that the placers were overrun by a crowd of gold hunters from California and Oregon, and that large bands of prospectors were spreading over the adjacent territory. Swift on the heels of this came the rumor that new placers had been found at Deer Lodge, on the east side of the mountains.
The idea was readily adopted that the country was filled with gold placers,—that it was not necessary to pursue the track of actual discovery, but that each man could discover his own mine. Thus believing, the stream of emigration diverged,—some crossing the range to Fort Lemhi on the Lower Salmon, and others pursuing a more southerly course, with the hope of striking an old trail leading from Salt Lake to Bitter Root and Deer Lodge valleys. Some of this latter party remained on Grasshopper Creek near the large cañon, where they made promising discoveries. The others went on to Deer Lodge, but being disappointed in the placers there, rejoined their companions and gave to their placer the name of Beaver Head Diggings,—that being the name given by Lewis and Clark to the river into which the creek empties.
While these discoveries were in progress on the east side of the mountains, a prospecting party which had been organized at Florence under the leadership of a Californian by the name of Grimes, discovered the mines on the Boise River. They were one hundred and fifty miles south of Florence. Grimes and his party sunk their first shaft fifteen miles northwest of the site of Idaho City. While preparing to extend their explorations, they unfortunately fell into an Indian ambuscade and their leader was slain.
Intelligence of the Beaver Head and Boise discoveries unsettled all local projects for building up the towns of Florence, Elk City, and Oro Fino. They were immediately deserted by all who could leave without sacrifice. West Bannack, at Boise, and East Bannack, at Beaver Head, sprung into existence as if by enchantment.