Cal. Const. art. XIII, § 2

The Legislature may provide for property taxation of all forms of tangible personal property, shares of capital stock, evidences of indebtedness, and any legal or equitable interest therein not exempt under any other provision of this article. The Legislature, two-thirds of the membership of each house concurring, may classify such personal property for differential taxation or for exemption. The tax on any interest in notes, debentures, shares of capital stock, bonds, solvent credits, deeds of trust, or mortgages shall not exceed four-tenths of one percent of full value, and the tax per dollar of full value shall not be higher on personal property than on real property in the same taxing jurisdiction.