Besides the border, what is another symbol in Luis Urrea's book The Devil's Highway?

The Devil's Highway, by Luis Alberto Urrea, is the true story of twenty-six men who attempted to cross the United States-Mexico border. Because of the tragic events of their journey, the entire group is now known as the Wellton 26, and those who lost their lives in the crossing are now known as the Yuma 14. Each of them wanted something more and was willing to work hard for it; this promise of something better is why they crossed the border and why the border serves as an excellent symbol in the book.

Twenty-three of the Wellton 26 are walkers; the other three are guides. In the illegal border-crossing world, these human smugglers are known as Coyotes. Coyotes are a symbol of exactly how illegal immigration works. The Coyotes are the men who have direct contact with the walkers and are ultimately responsible for them. In the animal world, coyotes are aggressive, nocturnal, opportunistic, predatory, and carnivorous; each of these attributes also applies to human Coyotes.

Coyotes are mercenary and Urrea calls them "stone-cold pragmatists" (chapter 3). These men, often much younger than the walkers they are leading, are merciless in their treatment of the illegals in their groups. Because they travel illegally and through the desert, they primarily travel at night. If a Coyote sees a chance to make more money, he does not hesitate to capitalize on it. (In this story, Mendez takes money from all his walkers, promising to buy water and bring them help; instead, he walks away and clearly has no intention of returning or sending help.) Figuratively, Coyotes are carnivores who feast on the illegals they transport by such acts as stealing, raping, and callously leaving walkers behind to die in the desert. Coyote is a perfect symbolic term for these mercenary human smugglers. 

"Three guides [Coyotes] led the Wellton 26 into the desert: one will forever remain anonymous [because his body was never recovered], one is only known by a code name [he died of hyperthermia], and one became infamous in the borderland." The lone surviving Coyote, known as Mendez, is in an Arizona jail for the rest of his life. Despite the cautionary tale provided by this story, Coyotes still roam the border looking for prey.