Cal. Code Regs. tit. 18 § 15905
If the tax is not paid on or before the last day prescribed by law for filing the quarterly gift tax return, i.e., on or before the 15th day of the second month following the close of the calendar quarter in which the gift was made, the tax becomes delinquent and thereafter accrues interest until the tax and interest are paid in full.
The Controller may, for good cause shown, extend for period not to exceed 6 months, the time for filing the gift tax return. (See Revenue and Taxation Code Section 15652.) However, the granting of an extension of time for filing the return does not extend the time for making payment. (See Section 15681). Even though an extension of time for filing the return is granted, the tax is delinquent if not paid on or before the original due date for filing the return. (See Revenue and Taxation Code Section 15962).
If the Controller determines a deficiency, upon his examination of a return filed at any time, the unpaid balance of gift tax due is delinquent from and after the last date prescribed by law for filing the quarterly return. (See Section 15961).
NOTE: Reference: Section 15905, Revenue and Taxation Code.
Cal. Code Regs. Tit. 18, § 15905