Many jurisdictions allow "in-person absentee" voting before the election day. In California this is after registration closes any time up to 8 pm on election night. You will need to present yourself at the county voter's office (in Alameda County this is the Registrar of Voters office in beautiful downtown Oakland - see http://www.acgov.org/rov) or at another authorized location. (I seem to recall that the Berkeley City Clerk's office used to be one ... maybe it still is.)
You fill out your absentee ballot app, hand it to the worker, and then go into the polling location they have set up.
Your county office may have special opening hours the weekend before the election for the convenience of the public. Check your local listings for details.