Just make sure it covers you on rentals in California. Some travel insurance doesn't work absolutely everywhere. And California law requires liability insurance for anyone who drives a rental there, with possibly quite bad consequences if you don't have liability insurance that's valid there:
Also: Is proof of your liability travel insurance that you carry with you in English? If not, is an English translation available? If stopped, you have to prove you're covered to the officer. Given that in some countries (relative to your home country) you may need an "international driving permit" (in addition to your local driving license), which is mostly a bunch of translations, I can imagine that a translation of proof of insurance might be needed in some cases.