Vote-by-mail ballots that are postmarked on or before Election Day or is time stamped or date stamped by a bona fide private mail delivery company on or before Election Day, and received by the county elections official shall be considered received on time. (Election Day for THIS election is 11/6/18.)
You can also drop off your ballot at any polling place in your county on Election Day, or before the election at a drop box in your county.
Ballot drop-off locations in Alameda County.
Ballot drop-off locations in Contra Costa County.