". . . this I can scarcely hope . . ."

Two days before reaching the Continental Divide, Meriwether Lewis speculated that the Columbia River would not have the same moderate character as the Missouri.
"I do not beleive (sic) that the world can furnish an example of a river running to the extent which the Missouri and Jefferson's rivers do through such a mountainous country and at the same time so navigable as they are.
if the Columbia furnishes us such another example, a communication across the continent by water will be practicable and safe. but this I can scarcely hope from a knowledge of its having in it comparitively (sic) short course to the ocean the same number of feet to decend which the Missouri and Mississippi have from this point to the Gulph (sic) of Mexico." — Meriwether Lewis, August 10, 1805.
Dividing the Waters of North America
North America's Rocky Mountains split the waters of the continent. To the east, the Missouri-Mississippi River system rolls placidly through the plains to the Gulf of Mexico. To the west, the Columbia River system roars to the Pacific through deep, narrow canyons filled with whitewater rapids.

How Did He Know?
Lewis estimated the gradients of the two river systems by this formula:
Gradient
= "Rise" (Elevation)/"Run" (Distance)

The Continental Divide at Lemhi Pass is 7,373 ft. above sea level. Water on its western slope runs about 600 miles to the Pacific Ocean. On the east side, water runs about 2,400 miles to the Gulf of Mexico.
Having reached the headwaters of the rivers, Lewis could use the formula at the left to calculate river gradients. He suspected the gradient of the Columbia River would be about four times greater than that of the Missouri/Mississippi Rivers.
As gradient increases, water flows faster. Lewis expected the rivers west of the Divide to be much swifter and more dangerous than the Missouri.

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"Immence (sic) Ranges of High Mountains Still to the West of Us..."
Agency Creek
Lemhi Pass
From Route ... To Road
Crossing the Great Divide
"Most Distant Fountain" of the Mighty Missouri
The Beginning of the "Endless Missouri"
Sacajawea Memorial Area
Sacajawea (Memorial Area)
First Idaho Campsite

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