How does Wallace Stegner use imagery in Beyond the Hundredth Meridian: John Wesley Powell and the Second Opening of the West?

Imagery:

"Losing one's right arm is a misfortune; to some it would be a disaster, to others an excuse. It affected Wes Powell's life about as much as a stone fallen into a swift stream affects the course of the river."

"But from the river bluffs where we have symbolically planted, himm, looking over the West that was his province, he can perhaps contemplate the truly vortical, corkscrew path of human motion and with some confidence wait for the future to catch up with him."