It should be noted that Steinbeck's Of Mice and Men is history as well as drama. The picture he painted of life on a California ranch is an old one. In the time he was writing about, the workers were mostly white males who drifted from place to place with the crops. There was a big influx of "Okies" and "Arkies" in the Dust Bowl era during the late 1930s. These were whole families, unlike the single, solitary men depicted in Of Mice and Men. Women and children worked in the fields alongside the men. These people were almost all white too. Steinbeck wrote about them in his classic novel Of Grapes of Wrath.
Then when World War II started in Europe in late 1939, the U.S. government began spending large amounts of money earmarked for "preparedness" and "defense." In California many good jobs became available, especially in shipbuilding, aircraft manufacture, and munitions manufacture, along with the subsidiary jobs in such things as transportation and warehousing. There was also a lot of bridge building, dam building, and highway construction financed by Roosevelt's New Deal programs. The white farm workers, including the new arrivals from the Dust Bowl, were absorbed by defense work, and when the U.S. was drawn into the war with the bombing of Pearl Harbor, many of the men were absorbed into the armed forces. There was a great shortage of farm labor, and the Mexican Bracero program was instituted in 1942 to allow Mexicans into the country on a temporary basis for as farm laborers. Since that time the majority of farm workers have been Mexicans. There has also been a changeover to sophisticated farm machinery, so that the teams of horses described in Of Mice and Men are no longer to be seen. The war ended the Great Depression and America enjoyed boom times which created abundant employment for white males. They never returned to farm work in significant numbers.
So Steinbeck's Of Mice and Men reads almost like a piece of nostalgia today. Steinbeck uses the setting in that novella to show the emptiness and competitiveness that existed among working men during the Great Depression. His settings are extremely simple because he wrote his novella with the intention of adapting it into a stage play. The main sets are a bunkhouse and the barn where Lennie kills Curley's wife. The only exterior setting is the riverbank campsite. The interactions of the characters are of far more importance than the settings. Steinbeck made much greater use of settings in his panoramic novel The Grapes of Wrath, where the reader experiences life on the highway and in roadside camps with the homeless Joad family.