Steinbeck's main theme has to do with the hard and hopeless lives of itinerant farm workers in California. The book has only four settings. They are the campsite by the river, the bunkhouse, the barn, and Crooks' room which is attached to the barn. The bunkhouse gets the most description because so much of the action takes place there.
The bunkhouse was a long, rectangular building. Inside, the walls were whitewashed and the floor unpainted....Over each bunk there was nailed an apple box with the opening forward so that it made two shelves for the personal belongings of the occupant of the bunk....Near one wall there was a black cast-iron stove, its stovepipe going straight up through the ceiling. In the middle of the room stood a big square table littered with playing cards, and around it were grouped boxes for the players to sit on.
The living accommodations for the workers are not much better than those in a concentration camp. They don't even have chairs but have to sit on upturned wooden boxes. The mattresses are burlap sacks stuffed with straw. Evidently the men have to bring their own blankets with them--and there are no sheets or pillow cases. Obviously the owners of the ranch care very little about the workers. They can take it or leave it. And they take it because they have no other choice. They wash in metal basins outside the bunkhouse and probably have to use an outhouse.
Crooks has to live by himself because he is black and a victim of racial prejudice. He sleeps in a room full of leather harnesses and other tackle, and he sleeps in a long box filled with straw. Steinbeck describes the possessions Crooks has accumulated to pass his time alone. He reads books and old magazines. His situation is worse than that of the white workers, but he is probably lucky even to have a roof over his head. He is not only black but badly crippled. It would be impossible for him to find other employment. He is stuck here, and he is afraid they may not keep him much longer.
The outdoor setting by the river is intended to show that these "bindlestiffs" are like hobos. They carry their bedrolls on their backs and travel on foot or by hopping freights. They sleep on the ground. They cook over campfires and use tin cans for cooking and eating.
The barn is just a barn and has no particular significance, except that this is the place where Lennie kills Curley's wife and where the men find her body.
Steinbeck wrote the short novelette with the intention of adapting it to a stage play immediately. That is why he has almost everything happen indoors. The play was produced in New York in 1937, the same year the book was published. It must have been a low-budget stage production, because the settings were minimalistic. The scenes by the river were probably represented by a fake campfire lighted by colored globes, with the rest of the stage in darkness. The barn was probably represented by a few bales of hay and a little loose hay scattered around on the floor. Crooks room was probably just a portion of the stage which had a few pieces of furniture, some reading material, and some harnesses hanging on a wall. His "room" could be lighted when the action was taking place there and left dark when the action was taking place in the side representing the "barn." The bunkhouse would have been the main setting. All it required was probably four double-decker bunks and a big table with some upturned boxes around it.
The intention of all the settings was to convey the impression that these men led miserable lives and had no hope for the future. The American people were becoming interested in the lives of the downtrodden because of the general spirit of the Great Depression. There was a feeling that something had to be done to change things. It was disgraceful that men should have to exist this way in the richest, most bountiful country on earth. That was Steinbeck's message, just as it was in his more panoramic novel The Grapes of Wrath.