Most of the book takes place in the Yukon Territory, the section of Canada buttressed up against Alaska. It was a pretty wild area, sort of the last hurrah for the Western frontier where men were men and guns solved arguments—or at least ended them.
It was full of big mountains, wide rivers, and the kind of stark beauty that you really want to visit until you realize the sheer number of ways you can get killed there. And yet, in the 1890s when the novel is set, it became a very popular place. Gold was discovered in 1896, prompting an influx of about 40,000 people looking to strike it rich. That explains what nice clean-cut white boys like Weedon Smith are doing up there, as well as unrepentant scumbags like Beauty Smith. The ones who had been there longer "called themselves Sour-doughs, and took great pride in so classifying themselves" (15.1). Apparently these guys used to keep their sourdough bread warm through the winter by storing it next to their bodies. Cozy?
The gold rush only lasted a few years. In 1899, gold was discovered in nearby Alaska, and everyone pretty much packed up their circus tents and moved there (or went home, like Scott does). London makes the Yukon a viable historical location, but also a neat balancing point between the wilderness and civilization, which is perfect for a journey like White Fang's.
You can see that most vividly during his journey to Fort Yukon, where "every two or three days a steamer (another and colossal manifestation of power) came into the bank and stopped for several hours. The white men came from off these steamers and went away on them again. There seemed untold numbers of these white men" (15.20). For Yukon sits right on the edge of the wild, and yet it's full of men who come and go, bridging the gap between the Wild-with-a-capital-W and Civilization-with-a-capital-C. Once he gets on that steamer
The last section of the book takes place in California, which is much warmer and gentler than the Yukon. Scott and his family live on a nice estate, full of good food and nice company where "White Fang lived fat and prosperous and happy" (24.1).
San Francisco is busy, but civilized (a little too civilized for White Fang, who sees it as a "nightmare" 22.3), and the white men seem to have everything more or less in hand. The contrast to the Yukon gets even stronger when you think that California itself as "uncivilized" just a few decades before the book takes place.
Deliberate irony, or object lesson? We're thinking object lesson: a land that used to be so wild and now is so civilized makes the perfect end for London's out-of-control wolf who learns to be happy serving a good-hearted do-gooder.