What do the descriptions of life in the Santa Clara Valley tell about Buck's original home?
Life with Judge Miller in the Santa Clara Valley is described as idyllic and lordly for Buck; he goes where he pleases, "commands" the other dogs and animals (as well as humans, in his own mind), and is in prime physical condition. The Judge and his family require nothing of Buck, and he has no responsibilities or real challenges to his easy lifestyle.
During the four years since his puppyhood he had lives the life of a sated aristocrat; he had a fine pride in himself, was even a trifle egotistical, as country gentlemen sometimes become because of their insular situation.
In literary terms, London is setting Buck up to fall hard and fast. He knows nothing of the evil men can do, nor the rigors of a hard life, nor challenges from other dogs as large and powerful as himself, if not moreso. However, Buck is also in good shape, and intelligent, so we have hope that he will not simply be dominated and helpless in the world he is about to be thrust into.