Private boating is a hobby that experienced river guides and adventurous individuals turn into their passion. The first step is to buy your own PFD. Soon you will be and borrowing friends boats which will eventually lead to a warehouse full of rafting equipment and no retirement savings. As a private boater, you'll need to find you own shuttle drivers, rafts, permits, and friends.
There are several great resources that have information about paddling California Rivers. Bill Tuthill has probably made the most comprehensive site with river descriptions at California Creekin'. The dreamflows river flows page also includes an online guidebook to several more difficult California runs.
Podcasts and YouTube Channels
Disclaimer: River descriptions and classifications may change due to natural events that may create new hazards or flows. C-W-R advises that any paddler that uses this site be additionally informed by seeking out local news and updates for changes on this river.