What is La Bestia in the novel, American Dirt?

La Bestia, or the Beast, is a series of freight trains that carries goods throughout Mexico. Following the tightening of immigration laws, migrants from Central America began illicitly boarding the train in hopes of getting to el norte. Yet, this endeavor holds all sorts of perils: "The possible manners of death available on La Bestia are all gruesome" (95). Migrants have been crushed between trains, lost limbs, slipped to their deaths, been attacked, kidnapped, and/or sold by human traffickers.