What elements of the narrative indicate that it is based on research?

Although this is a fiction story, the story could have happened. The Yukon gold rush of 1896 was real; the conditions of the trail to get inland to the gold mines and gold claims were real. The idea that the people who really made money were those who sold products to the miners is real. London himself went to the Yukon and did real life research in the sense that he participated in the rush itself.