Cal. Code Regs. tit. 18 § 15651.2
The donor's gift tax return must be filed with the Inheritance and Gift Tax Division of the State Controller's office at Sacramento on or before the 15th day of the second month following the close of the calendar quarter in which the gift was made. That is, May 15 for gifts made January 1 to March 31, August 15 for gifts made April 1 to June 30, November 15 for gifts made July 1 to September 30, and February 15 for gifts made October 1 to December 31.
The return cannot be filed prior to the close of the calendar quarter in which the gift was made unless the return is for a deceased donor, except where special permission is granted by the State Controller.
When the date for the filing of the return falls on a legal holiday, the filing date will be the day next following which is not a legal holiday.
A duly executed return placed in an envelope which is properly addressed to the Inheritance and Gift Tax Division of the State Controller's office at Sacramento, with postage paid, and deposited in the United States mail, will be considered as having been filed on or before the filing date if the envelope is postmarked prior to midnight of the due date for filing the return even though the return is not actually received until a subsequent date.
Whenever in his opinion good cause (such as illness or absence from State, place of business, or place where records are kept) exists therefor, the State Controller may extend for a period not to exceed six months, the time for filing the return. No extension will be granted until there is filed with the Controller either before or after the date for the filing of the return a verified application setting forth the reason or reasons necessitating the extension.
NOTE: Reference: Section 15651, Revenue and Taxation Code.
Cal. Code Regs. Tit. 18, § 15651.2