I don't know about California, but what I hear from my local utility in WA is that absent specific circumstances that make basic above ground wiring infeasible, undergrounding has to be paid for by the customers served, it can't be paid by general revenues as is the case for repair and maintenance.

We're mostly seeing service disruptions from downed lines and not wildfires though. Fire safety requirements might be grounds for general funds to pay for undergrounding, but you'd really need to check with the state regulations.

The customers are going to pay. The company will notionally take out the bonds, but the dollars will have to come from the customers...