Remember that the mad dash westward with wagon trains of folks started in 1849 with the California Gold Rush.The really big changes came after that.
The Lewis and Clark journals, filled with amazing stuff, were most amazing to me regarding grizzly bears, which they didn't even know existed in 1805. Moreover, when the Mandan Sioux told them about the bears, they wrote things in their journals belittling the Sioux about their fanciful tales. But well before arriving at the continental divide, Lewis wrote that he'd rather face 20 Indian warriors than one of those damned bears again. In fact, Lewis got shot in the ass by one of his men during a dust up with a bear on an island in the Missouri River that they stayed on one night particularly because they thought it would keep them from the bears.