The Actual Heights

Lewis and Clark's Measurements

Detail from Clark's 1814 Map

To see labels, point to the map.

Interactive map showing place names on Clark's 1814 map

Library of Congress

The map of the Northwest that William Clark drew to accompany Nicholas Biddle's paraphrase of his and Meriwether Lewis's journals was engraved by Samuel Lewis (1754?-1822; no relation to Meriwether), a draftsman and engraver in Philadelphia.1 It was one of the most important outcomes of the expedition, at least in the short term, for it supplied a new cartographic picture of Northwestern geography that served travelers until after the middle of the 19th century.2

In this detail, Clark's "26" refers to the "Upper Pitch," later called Black Eagle Falls, which he measured at precisely 26 feet, 5 inches. The figure "47" refers to the "Beautiful Cascade," later named Rainbow Falls, which he calculated at 47 feet 8 inches.

The third figure stands for the "Great Falls," shown in Clark's sketch as 87 feet and three-quarters of an inch in height. In his route map for June 13-July 16, 1805, it apparently was first written as "97 feet ¾ of an inch," with the nine later modified to read as an 8. It is also 87 feet ¾ of an inch in the maps Clark prepared in 1833 for Prince Maximilian.3 However, in Clark's 1810 manuscript draft of the simplified 1814 published version, it is clearly written "97 feet." Upon first seeing the fall on 13 June 1805, Lewis estimated its height at eighty feet. A party of tourists who visited it in 1868 understood the height was 84 feet. The Stevens Railroad Survey of 1853 declared it to be 76 feet,4 and although the engineer who designed the first dam that was built at the upper fall in 1890 announced that the actual height of each of the falls "did not vary six inches from the measurement given by Capt. Clark the engineer of the expedition,"5 when the Ryan Dam was built in 1940, the working height of the fall was measured as 78 feet.

How high are the falls, really?

Profile of Water Surface of the Missouri River

Lower Portage Camp to Black Eagle Dam

Diagram showing the pitch of the Great Falls of the Missouri

The accurate measurement of a series of falls, cascades and rapids as complex as the Falls of the Missouri is correspondingly complicated. William Clark estimated the total descent at 360 feet, 2-3/4 inches, which was close enough for simply descriptive purposes. For specific practical purposes, such as the development of water power to turn turbines that produce electricity, other factors must be considered.

This diagram is based on a drawing prepared in 1909 for the Great Falls Water Power and Townsite Company by an engineer by the name of Charles T. Main. The scale along the bottom margin indicates the distance in thousands of feet from the Great Fall upstream to the upper fall (Black Eagle Fall) and downstream to the vicinity of the lower portage camp. The crest of the Black Eagle Dam defines the upper limit of the "head," or column of water pressure that ends at the "tail water." The head is the total height, expressed in feet, of the column of water between the the crest of Black Eagle Dam and the tail water. In 1909 the potential head at the falls of the Missouri totalled 473 feet, more than twice the head of water available at the Niagara Falls.

In the first decades of the nineteenth century the technology for harnessing water power was limited to an output of less than ten horsepower per water wheel. Lewis and Clark could scarcely have imagined the engineering necessary to harness the power of the falls of the Missouri. Look at it this way: The principle of the dynamo was discovered in 1830. Clark, who may not even have heard of it, was sixty years old; Patrick Gass was 59; Nathaniel Pryor, 58; Alexander Willard, 52; George Shannon, 51. Not until sixty years later would electricity be produced by turbine-driven generators. When the first Black Eagle Dam was completed in 1890, it worked on a pressure head of only 39 feet. Part of its output was used to produce some direct-current electricity for local use; the rest was mechanically transmitted to riverbank factories in the old-fashioned way–by means of rope drives.

And how did Clark measure those falls' height?


1. Donald Jackson, ed., Letters of the Lewis and Clark Expedition with Related Documents, 1873-1854 (2 vols., Urbana: University of Illinois Press, 1978), 2:603n.

2. The importance of Clark's 1814 map is summarized in Gary E. Moulton, ed., The Journals of the Lewis and Clark Expedition (13 vols., Lincoln: University of Nebraska Press, 1983-2001), 1:13. See also John Logan Allen, Lewis and Clark and the Image of the American Northwest (New York: Dover, 1975), 375-376. In this detail, the "13 M" may be an engraver's error. According to Clark's survey the portage route was eighteen miles long. Clark's original draft, drawn in 1810, merely indicated a double dotted line labeled "portage."

3. Moulton, Atlas map 54. The Clark-Maximilian map that includes the falls is Atlas map 61.

4. Isaac. I. Stevens (1818-1852), Narrative and Final Report of Explorations for a Route for a Pacific Railroad, near the Forty-Seventh and Forty-Ninth Parallels of North Latitude, from St. Paul to Puget Sound (Washington, D.C.: Thomas H. Ford, 1855), 173.

5. Paris Gibson, "The Falls of the Missouri—Their Past, Present and Future," Rocky Mountain Magazine, Vol. 1, No. 1 (September 1900), p. 24.

6. Unpublished document, Montana Power Company, "Description of Hydroelectric Plants," p. 69.