May 23, 2016 (San Diego) If you plan to vote in the June 7 election, today is the last day to register. You can register by following this link.
If you plan to vote in the Republican Primary, this is not open. You need to be a Republican. If you intend to vote in the Democratic primary, it is a semi open primary. You need to either be a Democrat, or decline to state voter.
If you are a decline to state voter you need to request a partisan ballot when you go vote. It is too late to do it by mail. Though you can vote early at the Registrar of Voters