Read this excerpt from The Call of the Wild by Jack London. At the first step upon the cold surface, Buck's feet sank into a white mushy something very like mud. He sprang back with a snort. More of this white stuff was falling through the air. He shook himself, but more of it fell upon him. He sniffed it curiously, then licked some up on his tongue. It bit like fire, and the next instant was gone. This puzzled him. He tried it again, with the same result. The onlookers laughed uproariously. What does this excerpt reveal about the setting of the story?