Lonesome Dove, Volume 1 by Larry McMurtry

THE MEN BEGAN TO TALK of the Yellowstone River as if it were the place where the world ended-or, at least, the place where the drive would end. In their thinking it had taken on a magical quality, partly because no one really knew anything about it. Jasper Fant had somehow picked up the rumor that the Yellowstone was the size of the Mississippi, and as deep. All the way north everyone had been trying to convince Jasper that it didn't really make any difference how deep a river was, once it got deep enough to swim a horse, but Jasper felt the argument violated common sense. The deeper the river, the more dangerous-that was axiomatic to him. He had heard about something called undercurrents, which could suck you down. The deeper the river, the farther down you could be sucked, and Jasper had a profound fear of being sucked down. Particularly he didn't want to be sucked down in the Yellowstone, and had made himself a pair of rude floats from some empty lard buckets, just in case the Yellowstone really did turn out to be as deep as the Mississippi.

"I didn't come all this way just to drown in the last dern river," Jasper said.