"Justices of the California Supreme Court and California Courts of Appeal must run for retention in the first gubernatorial election after they are appointed and then every 12 years, when their terms expire, in November. In these elections, justices do not compete against another candidate. Instead, voters are given a "yes" or "no" choice as to whether to keep the justice in office for another term. The justice must receive a majority of "yes" votes to remain in office. If a justice is not retained, the governor appoints a replacement who must run for retention in the next gubernatorial election following their appointment.Justices are typically retained. Since the state started its system of retention elections in 1934, the only year that any supreme court justice was not retained was 1986. That year, three justices were ousted from the bench due to ruling against the death penalty. In 2010, all of the justices who faced retention were retained. Supreme court justices were retained by an average of 66.8% of votes, while justices of the intermediate appellate courts were retained by an average of 71.0% of the votes."
Judgepedia also lists who's up for election here.
Now is the time to plan to vote and to encourage everyone you know to vote too.