Answer:
The detail of the setting that causes the key conflict in this excerpt is "the piece of iron." The protagonist's sacred dream directs him to find something belonging to the white people and he finds the broken shell of an iron kettle, which reinforces his dream. However, the fact that the piece of iron belongs to the enemy, the white people, creates a conflict for the protagonist and raises questions about how he can reconcile his vision with the tribal beliefs and values of his people. This conflict sets up the central tension of the story and drives the narrative forward as the protagonist grapples with the meaning and significance of his discovery.