John Steinbeck was not a highly successful author in 1937 when he wrote Of Mice and Men. He did not expect much success because he was not writing the type of book that had big sales. Instead of courting popularity with romance and action-adventure, he wrote about poor working men in depressing conditions. When he wrote Of Mice and Men he was thinking of adapting it into a stage play. It can be seen throughout the novella that he was emphasizing dialogue to convey information and keeping the sets to a bare minimum. The campsite at the riverbank in the first and last sections could be represented by not much more than an imitation campfire electrically lighted with the stage dark around it. The main sets at the ranch are only a big room representing a bunkhouse and a barn where Lennie kills Curley's wife. The men eat offstage and work offstage. They play horseshoes offstage, and Steinbeck describes only the clink of an occasional "ringer." The horses are never seen but only represented by their jingling harnasses and stomping hooves.
The novella was a big success, and the play which was produced the same year on Broadway was also successful. This resulted in the story being further adapted into a motion picture in 1939. The excellent movie version starring Burgess Meredith and Lon Chaney, Jr. "opens up" the story by showing what is conspicuously lacking in the book and the stage play. The movie version shows the beautiful California farmland with men working in the fields and big wagons being pulled by the teams of horses which are only mentioned in the book but never shown.
It would be untruthful to say that Steinbeck's book "is set in the beautiful Salinas Valley in California," because it is mainly set in a bunkhouse and a barn, plus a sandback by a river.