Because this work is primarily carried by dialogue, the writing reflects the personality and speech patterns of the workers. Steinbeck is careful not to be too "high-falutin'" with his language or ideas.
But occasionally, when character and circumstance permits, Steinbeck lets his poetic self hang loose. We see this whenever Doc Burton waxes philosophic on mankind, for example, or when Steinbeck steps back and takes in the bigger picture. Here's an example:
The moment he stopped talking a turbulence broke out. Shouting and laughing, the men eddied. They seemed filled with a terrible joy, a bloody, lustful joy. Their laughter was heavy. (104)
There's no way that London or Dakin would ever use the verb "eddy," nor would they come up with a fancy oxymoron like "terrible joy." However, we're pretty glad that Steinbeck sneaks this poetry into such a bleak landscape, just to spice things up a bit.