Folklore, Legend, and Mythology; Pastoral; Tragedy
Okay, okay: we know that besides the tragedy, some of these genres might seem like a bit of a stretch. So let's start with the easy one. Tortilla Flat is a tragedy because Danny, the protagonist, is killed at the end as a result of overpowering and contradictory forces of adulthood during the Great Depression, which drive him to drink and ultimately die.
That's about as tragic as it gets. Any objections?
We didn't think so.
So, moving on: why would we connect this story with folklore, legend, and myth?
Well, to begin with, we'd make the connection because Steinbeck himself, in the novel's preface, compares his story to the legends of Arthur and Robin Hood: "It is well that this cycle be put down on paper so that in a future time scholars, hearing the legends, may not say as they say of Arthur and of Roland and of Robin Hood—'There was no Danny nor any group of Danny's friends, nor any house [...]' This history is designed now and ever to keep the sneers from the lips of sour scholars" (Preface.2).
So, no, these aren't exactly traditional stories passed down through the ages, but Steinbeck is drawing on folkloric and legendary genres to create his novel. He could be showing us that heroes are ordinary folks, too (or vice versa). He might also be showing us that every life is significant, even if the person living it is a poor, ordinary drunk.
Finally, Tortilla Flat has some pastoral elements, too. Tortilla Flat is definitely idealized in this novel: in contrast to Monterey, Tortilla Flat's "streets are innocent of asphalt and the corners free of street lights" (Preface.3). Using words with positive connotations, like "innocent" and "free," to describe Tortilla Flat make this neighborhood seem like a really wonderful place in contrast to the big, modern city. It's idealized and kind of innocent, just like the forest in stories about Robin Hood.