Too big of a lake and I am too far away and too unfamiliar with what's out there for help from me..But I'm sure there are very doable things for your problem. You basically need to work at correctly and properly diversifying the forage base. They do grow big bass in CA. I recommend you hire a "local" professional fishery biologist for some advice. Money should be well spent if he amounts to anything, has a track record and comes with references. Check them out first before hiring him for a few hours of work and advice.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management