In San Diego,. we complete a form and then have an agent pull all the recent market comparables. This then goes to the asessor's office for review.
The process of value reductions via Prop 8 is covered in this blog post:
"Estimating Property Taxes in CA"
Note that each year the Assessor compares the factored Prop 13 base year value to the current year Jan 1 market value after applying the California State Board of Equalization CA Consumer Price Index increase and uses the LESSER of the two figures.â€