If you are willing to take a “little bit of risk”, you can open an account with Vanguard and keep your money in VANGUARD CA LONG-TERM TAX-EXEMPT mutual fund (VCITX). You will recive 4.35% yield that is largely exempt from federal and CA taxes ( so it could be something like 6.9% pretax if you are in 28% tax bracket). You can withdraw money any time.

There is some market risk here (For example in Feb and March the fund had some losses which it since then has recovered) but the risk is much less than stocks (or RE)