Cal. Rev. & Tax. Code § 2821
Any person filing an affidavit of interest may apply to the tax collector to have any parcel separately valued on the current roll for the purpose of paying taxes. A county may, upon approval of the board of supervisors, require that the applicant notify the property owner.
The application shall be made during the current fiscal year, and shall set forth the fact that a duly executed and recorded deed, purchase contract, deed of trust, mortgage, or final decree of court describes the parcel sought to be separately valued. A county may, upon approval of the board of supervisors, allow these applications between July 1 and March 31.
The application may request that the tax created by the assessment of personal property, or leasehold improvements, or possessory interests on the whole assessment be allowed to remain as a lien on the parcel sought to be separately valued.
If any lien not determined by the application of a tax rate on a valuation of property has been levied or placed on the whole assessment, the application may be accompanied by the certification of the taxing agency or revenue district authorized by law to levy or place the lien, setting forth the specific amount of that portion of the lien levied or placed on the whole assessment which is to continue to be levied or placed on the parcel sought to be separately valued.
The board of supervisors may provide that a parcel with a lien against it and other property, pursuant to the Improvement Act of 1911 (Division 7 (commencing with Section 5000) of the Streets and Highways Code) or the Improvement Bond Act of 1915 (Division 10 (commencing with Section 8500) of the Streets and Highways Code) will not be separately valued unless a request has been made to the agency levying the bond lien for a division of land and bond. A copy of the requested division of land and bond shall accompany the request for separate property tax valuation.
Any separations of property pursuant to this section are for valuing property for tax purposes only, and are not intended to create a legal building site or to supersede requirements pursuant to zoning, building, lot split, or subdivision ordinances.
Once created, an individual interest parcel may be entered as a separate assessment on subsequent assessment rolls until the time that ownership of the interest is conveyed or until the original applicant or his or her agent requests that the parcel be recombined.
Upon authorization by ordinance by the board of supervisors, the county may charge a fee for actual costs incurred for the processing of an application for separate assessment, and the initial and ongoing costs of separate assessment, billings, and mailings. Fees shall be subject to Chapter 12.5 (commencing with Section 54985) of Part 1 of Division 2 of Title 5 of the Government Code, and may be billed separately or prior to initial separate tax bills, or both, or collected on subsequent tax bills, and shall be deposited in the county's general fund.
Ca. Rev. and Tax. Code § 2821