I think some readers attach too much importance to the Great Depression affecting the lives of farm workers in Of Mice and Men. Wages were always poor and working conditions always bad on California ranches because the men were uneducated and unskilled. There were too many uneducated and unskilled men, and wages were forced down by the law of supply and demand.
The only thing that changed for white farm workers was that World War II started in Europe in 1939, and the United States government began spending lots of money for at least two reasons. One was to supply manufactured goods to Great Britain and later to the Soviet Union. The other was to build up our own defenses. The white farm workers left the fields because they could get much better-paying jobs right in California in ship building, aircraft manufacturing, munitions making, oil drilling and other areas. The influx of money created jobs in all non-defense areas, because the workers had money to spend. Then after Pearl Harbor was bombed on Decembr 7, 1941, the amount of money being spent on what was now called the war effort was tremendous. Besides that, the military absorbed millions of men from the labor force.
The ranchers had a big labor problem because the white workers left and never came back. The ranchers solved the problem by bringing in Mexican workers on variious kinds of bracero programs. After that the farm work was taken over by legal and illegal Mexican immigrants. The wages and living conditions were terrible, until Cesar Chavez organized the United Farm Workers Union.
Stephen E. Ambrose, a noted historian, has written a lot about the history of California, including about the great immigration of Okies and Arkies in the later 1930s. These people were farmers and wanted to work on the California ranches--but they were absorbed into the manufacturing sector because of the boom years enjoyed by California and the rest of the United States from around 1939 until late in the 1940s. The United States changed greatly because of the war. There was a pent-up demand for all sorts of manufactured goods after the war, so good jobs were still available--mostly for white workers--into the 1950s. The war changed everything.
Now agriculture is becoming mechanized, and there is no great demand for unskilled farm labor. Those big teams of horses no longer exist, because one tractor has the power of more than a hundred horses. There are farm machines to do everything. More and more people are going to high school and college because there is an ever-increasing demand for educated workers. There are no more so-called pick-and-shovel jobs, because a machine can dig faster than a hundred men. I believe that only about two percent of the American workers are employed in agriculture. At one time it was ninety-five percent, and most of these people lived on subsistence farms.
Of Mice and Men is a good novella, but it is not a good source of information about conditions in California during the Great Depression. Several of James M. Cain's very interesting novels are much better at portraying conditions in California. One of his best is Mildred Pierce, which was made into a movie starring Joan Crawford and more recently into a very good television series. Cain's Double Indemnity and The Postman Always Rings Twice are also good at representing the mood of the Great Depression, both as books and as movies.