Removing a traffic hazard from the Missouri River.1
Perhaps the best luck the Corps of Discovery had in the entire two years, four months and ten days it was en route, was that it didn't suffer any fatal encounters with hazards of this magnitude. Considering only as much of the tree trunk as can be seen in the photo above (at least one limb has already been sawed off), it was nearly six feet in diameter. If about thirty feet of the butt end of the trunk is visible, and if the tree is a cottonwood, then this piece of it weighed about five tons – dry! (Cottonwood weighs thirty-eight pounds per dry cubic foot). The entire tree may have weighed three or four times that much. Imagine the crews of the keelboat and the two pirogues dealing with snags like this.
On 31 March 1805 Meriwether Lewis wrote a long letter to his mother, Lucy Marks, from Fort Mandan detailing the daunting dangers he had faced on the Missouri River, and hinting at the anxiety that, even as a natural risk-taker, he was feeling in anticipation of rivers to come.2
One of those difficulties, the navigator never ceases to contend with, from the entrance of the Missouri to this place; and in innumerable instances most of those obstructions are at the sam[e] instant combined to oppose his progress, or threaten his distruction. To these we may also add a fifth and not much less inconsiderable difficulty, the turbed quality of the water, which renders it impracticable to discover any obstruction even to the debth of a single inch.
Such is the velocity of the current at all seasons of the year, from the entrance of the Missouri, to the mouth of the great river Platte, that it is impossible to resist it's force by means of oars or poles in the main channel of the river; the eddies therefore which generally exist one side or the other of the river, are saught by the navigator; but these are almost universally incumbered with concealed timber, or within the reach of the falling banks, but notwithstanding are usually preferable to that of passing along the edges of the sand bars, over which, the water tho' shallow runs with such violence, that if your vessel happens to touch the sand, or is by any accedent turned sidewise to the current it is driven on the bar, and overset in an instant, generally distroyed, and always attended with the loss of the cargo.
The base of the river banks being composed of a fine light sand, is easily removed by the water, it hapens that when this capricious and violent current, sets against it's banks, which are usually covered with heavy timber, it quickly undermines them, sometimes to the debth of 40 or 50 paces, and several miles in length. The banks being unable to support themselves longer, tumble into the river with tremendious force, distroying every thing within their reach.
The timber thus precipitated into the water with large masses of earth about their roots, are seen drifting with the stream, their points above the water, while the roots more heavy are draged along the bottom untill they become firmly fixed in the quicksands which form the bed of the river, where they remain for many years, forming an irregular, tho' dangerous chevauxdefrise3
1. From Hiram Chittenden, History of Early Steamboat Navigation on the Missouri River, 2 vols. (New York: Harper, 1903), II:420.
2. Donald Jackson, Letters of the Lewis and Clark Expedition with Related Documents, 1783–1854, 2nd ed. (Urbana: University of Illinois Press, 1978), 222–25. The original letter is at the Missouri Historical Society Library in St. Louis. (Re-paragraphed here for the reader's convenience.)
3. Properly, cheveux défrise (literally, "to straighten the hair"), a French-Canadian riverman's expression meaning hair-raising or frightening.
4. Chittenden, op. cit., II:421.