Symbolism, Imagery, Allegory
Paradise Lost
Since there’s something Eden-like about Buck’s original home in the Santa Clara Valley, we’re thinking it represents a sort of ideal, a paradise.
But you know what happens to paradise. It gets lost. Over and over again.
Buck's character goes through a dramatic change in this novel—he grows strong, he gets toughened, and he evolves into the wild wolf-dog he always had deep inside. It's necessary for Buck to leave the paradisaical confines of Santa Clara...so that he can exist as a well-rounded character.
Just check out the way he remembers Santa Clara once he's left:
Love, genuine passionate love, was his for the first time. This he had never experienced at Judge Miller's down in the sun-kissed Santa Clara Valley. With the Judge's sons, hunting and tramping, it had been a working partnership; with the Judge's grandsons, a sort of pompous guardianship; and with the Judge himself, a stately and dignified friendship. But love that was feverish and burning, that was adoration, that was madness, it had taken John Thornton to arouse. (6.3)
Buck isn't just going wild; he's also growing up. In this recollection, Buck's life in Santa Clara sounds like the pastel memories of childhood—the sun, the shallow relationships, and the sense of belonging without the sense of freedom that makes adult life so interesting and dynamic.