If you plan on using it with a motor of any sort it's gotta be registered. Take the hull identification number and fill out the forms at your local DMV or AAA branch. If you have a trailer, that also needs to be registered--the DMV requires you to bring the trailer in to record the VIN and manufacturer information.

Check the DMV link: http://www.dmv.ca.gov/boatsinfo/boatreg.htm