E-text
http://sunsite.berkeley.edu/London/Writings/CallOfTheWild
along with Concordance of the book.
Biography
http://sunsite.berkeley.edu/London/jack.html
A brief but thorough biographical essay on Jack London.
The California Gold Rush
http://ceres.ca.gov/ceres/calweb/geology/goldrush.html
This site, produces by the California Environmental Resources Evaluation Sysem, provides a concise summary of the history of the Gold Rush, as well as interesting links to other sites dealing in Gold Rush history.
The Gold Rush
PBS's website on the California Gold Rush provides historical and cultural information as well as resources for teachers.