The opening paragraph describes a serene scene in the Salinas river valley. This is an area south of San Francisco known for its ranches and agriculture. The story is set during the Great Depression, but the narrator never alludes to this. However, the reader does get a sense of the economic struggles that George and Lennie (and the other workers) have to endure.
In the opening scene, the water is "deep and green," "twinkling over the yellow sands," and down into a warm pool. "On the sand banks the rabbits sat as quietly as little gray sculptured stones." The mood at this point is peaceful.
The wildlife scurry away when George and Lennie approach. Each man is described as being the opposite of the other. George is small, defined, and quick. Lennie is large, shapeless, and lumbering. Lennie throws his head into the pool and drinks like a starved animal. George scolds him.
The rest of the chapter is devoted to the dialogue between George and Lennie. Lennie has been petting a mouse in his pocket. He doesn't know his own strength and kills the mouse. George orders him to throw it away. The mood is certainly less peaceful than that opening scene, but this is to show one of the conflicts in the novel. George is faced with taking care of a large, abnormally strong, socially awkward man. George has a quick temper and is always going off on Lennie. In spite of this conflict, they are extremely loyal to each other and their shared dream of owning a farm gives them the will to carry on.
Lennie constantly asks George to tell him about the rabbits and their future. He needs this constant reminder of optimism. George, sometimes reluctantly, abides and repeats the story. Other ranchers lead lonely lives, but he and Lennie have something going for them:
"With us it ain’t like that. We got a future. We got somebody to talk to that gives a damn about us. We don’t have to sit-in no bar room blowin’ in our jack jus’ because we got no place else to go. If them other guys gets in jail they can rot for all anybody gives a damn. But not us."
The first chapter ends with this optimistic mood. The two men fall asleep, having just discussed their dream. The final description of the setting reinstates a sense of peace to go along with that optimism:
The red light dimmed on the coals. Up the hill from the river a coyote yammered, and a dog answered from the other side of the stream. The sycamore leaves whispered in a little night breeze.