In California there is no automatic review/reduction process. Each case has to be appealed separately. That makes sense for the Assessor because it becomes a case of “unless otherwise directed”, where they’ll continue to collect the taxes until it’s decided otherwise.
What usually happens is the property owner files for the appeal and presents the appraisal or in some cases just the raw data to show that their property is currently overassessed. If the Assessor agrees or otherwise decides not to contest it they just go ahead and reassess the property based on the lower value. If the Assessor decides to fight it they get their valuation together and take it to a hearing.
The reduction in taxation isn’t permanent because the purchase price will always serve as the basis where the Prop. 13 limitations apply. So if a property loses 30% in value relative to its most recent purchase price the lower taxes will only apply for as long as the “loss” continues, and it is subject to annual adjustment up to where the adjustments to the prior purchase price take off – THEN the Prop. 13 limitations apply.
At any rate, since there is some time and effort involved in the appeal process, I wouldn’t anticipate that most homeowners would spend the money necessary to reduce their annual RE taxes until their potential savings get to be at least $1,000/year. Of course, during the last cycle when average home prices were 1/3 of what they are now and the overassessments were only measured in the $100s of dollars rather than the $1,000s of dollars there wasn’t too much appealing going on. Now with annual RE taxes for recent purchases starting at $5,000/year and up, it would only take a 15% hit in market values to make it worth these taxpayers while to appeal.
As an example, an $800,000 purchase of a new tract home in Carlsbad in 2004 would result in annual taxes of about $8,900/year. A 15% reduction in market value relative to that purchase price would justify a $1,335 reduction in taxes for however long it took for the market value to return to the $800k mark, at which point the Prop 13 limitations would hold the annual adjustments down to the 2%. If the market value went up 15% since then it would take a 30% loss (from today’s value) before that property owner had enough of a loss to make it worth their while to appeal.