Legal Question in Real Estate Law in California

First, the "mortgage holder" is not the borrower (you); it's the lender or the party entitled to repayment. Next, as to taxes, transfers from parents to children are generally exempt from property tax increases based on reassessment, but check with the county assessor for local details as to how to claim the exemption. These rules vary by county and I'm not familiar with El Dorado County. As to Federal taxes on any capital gain, consult your tax advisor, and/or have your advisor comment on whether there could be a gift tax liability based on the actual numbers involved. Finally, most lenders (mortgage holders) will not object to addition of a joint tenant to the title (not the "deed"), but since most mortgages (technically, promissory notes secured by a deed of trust) contain "due on sale" clauses, it's highly advisable to check with the lender/holder to verify that they don't object and do not require any additional paperwork or fees. So, three stops to ask questions: the assessor, your tax advisor, and the lender.