Fortunate Camp Observations
Fortunate Camp, as Lewis and Clark described it, was at the forks of the Jefferson River, for them the farthest point of navigation on the Missouri. It was there that they laid up their canoes and, having had the good fortune to meet the Shoshone and barter for horses, proceeded on more than 300 miles overland, crossing several mountain ranges, until they reached the forks of the Clearwater River in present-day Idaho.
The names that the captains gave these streams—East Fork and West Fork Jefferson River—do not appear on modern maps. Where were the forks of the Jefferson River?
Several means are available to resolve the question. The earliest known "investigators" were several perceptive fur trappers in the late 1820s and early 1830s, such as Warren Ferris, John Work, and Alexander Ross. Their method of identifying features that Lewis and Clark described was simply to read the 1814 edition of the journals and match the captains' descriptions with the geography they saw for themselves. By the 1830s the Jefferson River above its junction with the present-day Big Hole River and Ruby River already was called the Beaverhead River, and fur trappers had given the east fork of the Beaverhead River its modern name, Red Rock River. The west fork was first called Horse Plains presumably because Lewis and Clark traded for horses there with the Shoshones; its name was changed around 1865 to avoid confusion with another Horse Plains in northwestern Montana.
But how certain can we be that the identifications made by the mountain men were correct?
The simplest and surest way to identify these forks is to review Clark's maps and compare them with modern maps. Another way is to plot the expedition's river and route-survey data and compare the plot with modern maps. Both methods have been used, and they confirm the general location of Fortunate Camp. Additionally, by using maps and aerial photographs that pre-date the reservoir now covering the campsite, it appears that the coordinates for Fortunate Camp most probably were at or near 44°59'36"N, 112°51'43"W (1927 datum). Nevertheless, an important cross-check of the camp's location comes from an evaluation of the data that Lewis and Clark obtained from their celestial observations for latitude and longitude.