You can apply for a review

[(former)FormerSanDiegan]

You can apply for a review of assessment to the County.

Here is the brief explanation and form :

http://www.sdarcc.com/arcc/docs/calrev.pdf

However, if/when the value returns to or greater than the amount allowed by Prop 13 (the original basis + 2% per year), they can adjust the taxes back up. I first heard about people complaining about getting re-adjusted back to the original basis in about 2000.