Why didn't Chris travel farther than the Toklat River?

In Chapter 16, Chris decides to travel “no farther west than the Toklat River.” Previously in the chapter, his journey is described as “slow going.” This is in part because he spends most of his days “stalking animals” in order to feed himself. His journey is also “slow going” in part because his journey takes him through “a gauntlet of boggy muskeg and impenetrable alder.” One can infer from these quotations that Chris travels no farther than the Toklat River because he is tired and a little bit fed up. His journey becomes much more difficult than he expected, and so he decides not to go as far as he originally intended. Indeed, he describes his initial plans as “obvious folly.”
After he decides to go no farther than the Toklat River, Chris decides that he will make his base camp at the derelict “Fairbank bus 142.” He decides that “the wilderness surrounding the bus” is enough of a wilderness for him.