The State of California Franchise Tax Board says that if an S-Corp elected LLC is filing taxes for the first time it can do one of the followings:
1) File state taxes as LLC and attach the S corp election document
2) File state taxes as S corp, enter all zeros, ones or nines into the CA corp ID field and attach the IRS S corp election acceptance letter
The board will send you a CA corporate id to use during next year's filing.
So, as you can see, the CA corporate # is required, so if this is not your first year of filing the CA 100S, then you may need to call CA FTB to get a CA corporation #.
CA FTB says that an S corporation is a corporation that elects to be taxed as a pass-through entity.
A CA Corporation is required to have a corporation #.
If you make an election for your LLC to be taxed as an S corporation, then you take on all the requirements of an S corporation for tax purposes.
