They mail them a month ahead of time.
Developing countries where people struggle with food and sanitation have this figured out and California rightfully deserves to be mocked by them.
Voting is for adults and we don't need to cripple the system to cater to people so irresponsible they can't drop a piece of paper in a box on time. If that's too hard you don't deserve to vote or there is something more nefarious at play.