The humans in chapter 5 of Call of the Wild make the great mistake of venturing into a setting about which they know nothing, and they pay the price for that ignorance. They arrive in the Klondike with no knowledge of what supplies they need, no experience in how to pack a sled to transport those supplies, and no understanding of the critical impact the weather has on travel and other activities in the far north. Indeed, they may have thought that spring would be a great time to travel - in their old, more southern existence, spring was when snow melted and travel became easier because it was warmer.
The dogs are too tired and hungry to do anything but try to survive. Only Buck is able to summon the determination needed to refuse to advance into the thaw.