by Jim Wark
When the original (1891) Black Eagle Dam was replaced in 1928, the raceway, powerhouse, and tailrace permanently displaced the historic island and its avian population.
Commercial traffic on the Missouri River ended quickly with the completion of the first railroads across the northwest in the 1880s and 90s, so when the construction of dams began early in the 20th century—for flood control, irrigation and electrical power generation—there was no need to include locks through any of them. Today, pleasure boaters must portage around each of the fifteen mainstream dams on the Missouri, including the five at Great Falls.
Like all rivers in the Northwest, the Missouri is highest during spring and early summer, reaching its lowest ebb from late summer through late winter. This photograph, taken in October of 2003 following an unusually dry summer, reveals the underlying geology of the falls that Lewis deemed a "noble and interesting object." Significant advances had been made in the concept of stratigraphy, especially in America, even during the very years of the Lewis and Clark expedition, but the captains were unprepared to appreciate the history of those light-brown and red-brown sandstone layers beneath all the falls. Nor could they have yet known those rocks were 115-million-year-old products of the Cretaceous Period of the Mesozoic Era, when modern mammal and bird groups, along with the first flowering plants, also emerged. Later in the nineteenth century, geologists named these old riverbed sandstones the Kootenai Formation.1
1. Museum of Paleontology, University of California, Berkeley, http://www.ucmp.berkeley.edu/mesozoic/mesozoic.html/ Moulton, 4:288n. John C. Greene, American Science in the Age of Jefferson (Ames: Iowa State University Press, 1984), 218-252.