I think you may mean the episode in chapter 13 when Sal and Terry have hitch-hiked to Sabinal. They have been trying to find work picking grapes, without success. Sal lies on his back in the town square and repeats over and over to himself 'What'd he do up in Weed?' He's thinking of the 'picture' of Steinbeck's 'Of Mice and Men', with Burgess Meredith as George. Thus Sal is implicitly linking himself to the itinerant farm worker in Steinbeck's novel.