Cal. Code Regs. tit. 18 § 13556
The usual presumption that property acquired by a husband or wife after marriage is community property does not apply as against any claim by the State for the inheritance tax. The burden of proving any property to be community property is on the person who claims that it has such status. A claim that property is community property must be supported by form IT-3, entitled "Marital Property Declaration." This declaration should be executed by the decedent's surviving spouse, or if it is for some reason impossible for the surviving spouse to execute the declaration, by any person having actual knowledge of the facts required, and submitted to the inheritance tax referee or, if no court proceeding to determine tax is pending, to the State Controller. Copies of form IT-3 may be obtained from the referee or from the Inheritance Tax Division of the Controller's office in Los Angeles, Sacramento, or San Francisco.
NOTE: Reference: Section 13556, Revenue and Taxation Code.
Cal. Code Regs. Tit. 18, § 13556