The rest of the day went on just like the day before, and the day before that. Sam followed his brother as they inched their way through Chilkoot Pass, the worst part of the Klondike trail. It was this thirty-mile stretch that broke most gold-rush stampeders. Chilkoot was not only steep and narrow, but the brothers were each required to haul two thousand pounds of food and gear through its treacherous route. Failing to do so meant that the Canadian Mounties would send them home. So the pair pressed on, hauling packs for half a mile, setting them beside the trail and then going back for another, and another, and another. Sam guessed that they walked at least fifty miles for every mile they moved forward. What does the excerpt show about the historical context of the story?