" . . . one of the handsomest plains I ever beheld"
Meriwether Lewis wrote in his journal on April 25, 1805:
I ascended the hills from whence I had a most pleasing view of the country, perticularly of the wide and fertile vallies formed by the missouri and the yellowstone rivers, which occasionally unmasked by the wood on their borders disclose their meanderings for many miles in their passage through these delightfull tracts of country. . . . The whol face of the country was covered with herds of Buffaloe, Elk & Antelopes; the deer are also abundant, but keep themselves more concealed in the woodland. The buffalo Elk and Antelope are so gentle that we pass near them while feeding, without apearing to excite any alarm among them, and when we attract their attention, they frequently approach us more nearly to discover what we are, and in some instances pursue us a considerable distance apparently with that [in] view.
After leaving Fort Mandan the Corps of Discovery had passed through a "game sink" where animals were comparatively scarce, and now were entering a huge buffer zone between competing Indian tribes, a zone that historian Dan Flores has called "the American Serengeti."
On April 26, 1805, Lewis noted:
The Indians inform [us] that the Yellowstone River is navigable for perogues [30- to 35-foot rowboats] nearly to its source in the Rocky Mountains, and that in its course near these mountains it passes within less than half a day's march of a navigable part of the Missouri.
Fifteen months later Captain Clark would confirm that the Indians were about right. Most of the Yellowstone, at least as much as he saw of it, is navigable by boats about the size of the Expedition's pirogues. But it would take him two days to march from the three forks of the Missouri to the Yellowstone River at today's Livingston, Montana. It's 57 miles via modern Interstate 90.
Further Reading . . .
Paul S. Martin and Christine R. Szuter, "War Zones and Game Sinks in Lewis and Clark's West," Conservation Biology, Vol. 13 No. 1 (February 1999), 36-45.