Why was John Thorton camping by himself?

John Thorton’s partners left him to camp alone the previous December after he froze his feet. Before leaving him behind, his partners ensured that he was comfortable and could fare well on his own while his feet healed. They then traveled on to Dawson by river.
The dog Buck and his team, under the watch of the two men Hal and Charles, and the woman, Mercedes, chance on John Thorton’s camp on their way to Dawson. Buck’s team is weary and hungry, as their handlers are inexperienced dog managers. The team of dogs pulling the heavy load is not well rested and is underfed. The dogs also have to grapple with the inefficiency of their handlers, who do not know basic things such as how to set up or break camp. By the time the team reaches Thorton’s camp, it is totally demoralized and lacks the strength to get on with the journey. However, the three people in charge decide to continue their journey in spite of advice to the contrary. When Hal descends on the fallen Buck with a club, Thorton intervenes to protect the poor dog from its unkind master. This marks the beginning of a great relationship between the dog and Thorton, who then becomes its new master after its owners leave it behind. At the time of Buck’s rescue, Thorton is still limping from the frostbite that affected his feet.