In the novel, the border between the United States and Mexico is not just a border but a wall. Referred to as "el otro lado," or the other side, the border divides families forever. It separates both Adelina and Juana from their fathers and destroys their families.
For example, Adelina is looking for her father, who crossed the border nineteen years before. The man who is guiding her in her search tells her, "Your father was bitten by a snake. The coyote probably left him here thinking la migra would find him" (page 4). The father's snake bite is symbolic of the poison that the border injects into people, who are torn from their roots and identities when they cross. At the moment when Adelina is searching for her father, la migra, or the immigration authorities, arrive. This is an example of irony, as la migra arrives nineteen years late to help Adelina's father. Instead of being helpful, the immigration authorities only harass people trying to cross the border. The coyotes, or people who take money to help people cross the border illegally, prey on the people they are trying to help, much like real coyotes.
Later, when Juana is trying to cross the border, she hears a father speaking to his young daughter, who asks why they can't simply take the bus across the Mexican–US border. The father responds, "Because we don't have papers, Carmen. And even though it's just land, it represents a wall. We must go like thieves" (page 143). The father's speech highlights the fact that the border is artificial. Though immigrants are just crossing land, the border has become a wall, and because they are not always welcome, Mexicans are made to feel like thieves. Their identities completely change at the border, where they are no longer hardworking people looking for a better life, as Juana's father is, but instead are seen as thieves or criminals. The border forces them to think about their identities differently and turns even innocent children into thieves.