My question involves landlord-tenant law in the State of: California

Hi,
If a lease term ends and the tenancy reverse to month-to-month, what is the procedure for one roommate to leave? Can the leaving roommate just submit 30 days' notice directly to the landlord? Does the remaining roommate need to sign any addendum releasing the leaving roommate from the lease?

Edit: I should add that the leaving roommate is happy to let the remaining roommate have their portion of the security deposit.