How does James A. Michener use imagery in Centennial?

Examples of Imagery:

"That's the sorriest river in America. You've heard all the jokes about the Platte. 'Too thick to drink, too thin to plow.'"

"They came into the bright summer sunlight like slugs from beneath a rock, and what they saw reassured them: a lot of cowboys, a lot of local boobs waiting for the games, and especially a group of businessmen on the lookout for something good."