THere's a paddling club or two based out of the bay area, so I'd start by finding info on them. They run tuolemne (I probably spelled that horribly wrong) Merced and a lot of others in there.
I think California might have a similar Mountainbuzz type website, but I'm not sure. You can certainly ask the same question that you have here on Boater Talk and get a lot of direct replies form folks who know more than I do (but lack of knowledge never stops me from rendering an opinion!)
Good luck. California has some great boating. I'm just leaving the Cal Salmon today, actually.
"self-aggrandizing jackass" - it says it right on the label