Real Property Appraisal

Real Property Appraisal
Proposition 13 was passed by the voters in June 1978 and substantially changed the way that real property is assessed in California. The major changes included the establishment of a 1975 base year value for all properties.

Thereafter, the base year becomes the year in which the real property is purchased, undergoes new construction, or a change in ownership occurs. If none of these events occur, the assessed value of most properties will increase by no more than 2% per year.

Additional Details

Under Proposition 13, the property tax rate is 1% of the assessed value, plus any bonds or fees approved by the voters. An annual tax bill may also include other special assessments and levies which are not based on assessed value.

Assessment Responsibilities

State law requires the assessor to deliver the annual assessment roll to the auditor by July 1, the first day of the fiscal year. This roll is an official list of property values which provides the basis for the computation of the annual property tax bills.

The annual assessment roll includes both the secured roll and the unsecured roll. The secured roll contains approximately 38,000 assessments for taxable parcels of land and the improvements on them. The unsecured roll contains approximately 4,000 assessments of business personal property, boats, and aircraft.

Additional information regarding California property tax programs are available at the California Board of Equalization website.

Supplemental Assessments

State legislation (SB813) enacted in 1983 requires the issuance of a supplemental assessment, and subsequently, a supplemental tax bill as of the date of the change in ownership or completion of new construction. The supplemental assessment reflects the difference in value between the existing assessed value of the property and the new base year value established as of the date of the change in ownership or completion of new construction.


If one of these events occurred between January 1 and May 31, there will be two Supplemental Assessments, one prorated for the remaining months in the fiscal year that the event took place, and one for all of the following fiscal year. If an event occurs between June 1 and December 31, there will be only one supplemental assessment prorated for the remainder of that fiscal year.


Notices of supplemental assessment amounts are mailed to property owners to advise them of the new valuation of the property, the existing roll value, and the amount of the Supplemental Assessment. For more information regarding supplemental assessments, please call 209-533-5535.

Supplemental Assessments & New Construction

New construction can be excluded from a supplemental assessment if the owner notifies the assessor, in writing, within 30 days of the commencement of construction, that he or she intends to offer the property for sale and does not intend to rent, use, lease, occupy, or otherwise use that property.

You may download an application for a builder's exclusion, or for more information, call 209-533-5535.

New Construction

New construction is appraised either as of the date of completion or as of January 1 if it is under construction on that date. Removal of property is considered new construction and may result in a refund. Repair, replacement, and maintenance are generally not considered to be new construction.

The Assessor’s Office receives copies of all building permits issued with the county, including the City of Sonora. Our office independently determines the value of the new construction and adds it to the assessed value of the existing property.

Change in Ownership

The Assessor’s Office reviews all recorded deeds to determine which ones, by law, require reappraisal. Our office may also request additional information from the owner about a deed or other transfer document. The owner’s response is strictly confidential and is not available to the general public.

When it is determined that there is a reappraisal change in ownership, the market value of the property is established as of the date of the change in ownership. You may download the Preliminary Change in Ownership Report, which should be filed at the time that a transfer document is recorded.