I gave up my interest in our real estate property because it is underwater. I signed a Grant Deed transferring my interest to my wife as her sole and separate property. Since California is a community property state, will I still be considered an "owner" even if I have already given up my interest?
California is a community property state. Howvever, you maybe liable for the mortgage on the property. I advise you meet with a real estate attorney and discuss the specifics of your case.
As you indicated you relinquished your interest in the real estate that you owned with your spouse. This relinquishment of interest did not release you from your obligation to the lender. Your mortgage or loan agreement is a contract between you, your spouse (I assume) and your lender. It continues despite any arrangement that you make with your spouse. While you are no longer an owner it sounds like you are an "obligor" - borrower on the note secured by the real estate.
This is a general answer only and you should seek the advice of counsel to address facts specific to your circumstances.