Coast Guard would not be under direction of Calif. State Law. They're regulated by federal jurisdiction. I was wondering the same thing as you were about life vests. It would seem that there is no statute suggesting that they are mandatorily worn while tubing. If it were, the manufacturer would be obliged to mention it. In fact, the manufacturer only "recommends wearing a Coast Guard-approved life preserver" while using their product. You should really get one if you're gonna tube open salt water.