Cal. Code Regs. tit. 18 § 15906
The gift tax must be paid at the office of the State Controller, Inheritance and Gift Tax Division, in Sacramento, California. Payment may be made in cash or by check, draft or money order, made payable to the order of the State Treasurer of California.
The acceptance by the Controller of a check, draft or money order constitutes a payment of the tax for which it was given as of the date of acceptance when, but not before, such paper is actually paid. if the paper for any reason is not actually paid, the Controller will proceed to collect the tax, and the taxpayer will remain liable therefor, together with all penalties and interest thereon, as though the paper had not been tendered.
A remittance in payment of the tax which is sent to the Controller through the United States mail in a properly addressed envelope, with postage paid, will be treated by the Controller as if it had been received by him on the date shown by the post office cancellation mark stamped on the envelope.
NOTE: Reference: Section 15906, Revenue and Taxation Code.
Cal. Code Regs. Tit. 18, § 15906