Wolf
Billy's first venture in the novel is to return the she-wolf to her home in Mexico. As an Anti-Western, The Crossing takes place long after the end of the “wild” West. The she-wolf then represents the last vestige of wild nature leftover the West. The elements which have not been destroyed or dominated by man. Unlike civilized society, the wild, natural state ignores the borders of the land. The she-wolf represents the wild instinct which remains. A wild instinct which Billy seeks to preserve.
Parham Horses
The last remnants of the Parham brother's property. The horses, stolen and sold in Mexico, are the two's last links to their family. Along with the death of their family, the theft of the Parham horses represent another major loss in Billy's identity. Billy believes that only through their retrieval can they avenge their father. As Billy returns to Mexico (with Boyd) in his second “crossing” to rescue the horses. This though only leads them into even deeper danger and destroys the last of their relationship. They too are what is left of Billy's “civilized” instinct which was lost with the wolf.
Boyd
While Billy's brother is a major character in the book, he is also a major metaphor to Billy. Boyd comes to represent Billy's last, unspoken connection to society. With Boyd's death, Billy is left alone and isolated. His searching for Boyd's fate becomes a search for his own identity. If Billy can not retrieve Boyd, he can not retrieve himself. Billy's fate becomes as questionable as Boyd's identity in death.
The Dog
The last creature/character which Billy encounters, and interacts with, is a crippled dog in New Mexico. While the dog shows Billy only kindness, Billy drives the dog away for some reason. Miserable and broken, Billy can not accept the sad creature's kindness. The dog becomes the opposite symbol of the wolf: a sign of human society. Unlike the wild woof, the crippled dog is a total symbol of settled society. It seeks companionship which the wild Billy can no longer understand. By rejecting the dog, Billy rejects his civilized origins.
The Trinity Test
The “second sun” or light Billy witnesses from inside the barn at the end of the book. It illuminates the night and awakens Billy. The light is likely the July 16, 1945 “Trinity” nuclear bomb test. The existence of the bomb shows the total change of the world since Billy began his journey. The boy started it with the natural wolf, but ends it by the unnatural light of the nuclear bomb. The blinding light of the bomb shows the dominance of technology over the world. No longer is this the Wild West world of the wolf Billy tried to save. It has grown into a world of untamed technological warfare. Billy's own distance to the bomb (which he can not comprehend) is the same as his own distance to the civilized world he no longer understands.
