A magnitude 5.6 earthquake occurred on the Calaveras Fault on October 30 , 2007 at 20:04 PDT ( October 31 , at 03:04 UTC ) , near Alum Rock . Prior to the 2014 South Napa earthquake , it was the most powerful quake to hit the Bay Area since the Loma Prieta earthquake of 1989 , and the largest on the Calaveras Fault since 1984
magnitude 5.6 earthquake
2007 Alum Rock earthquake
Calaveras Fault