Over 55? California Property Tax Relief
Proposition 60 and Proposition 90
It does not pertain to every county.
If either yourself or if you have a spouse who is over age 55 (when your primary home is sold), PROP 60 allows replacement of a primary residence with a new home of equal or lesser value within the same county and transfer of the Prop 13 assessed valuation from the old home to the new property. This is allowed once in your lifetime, and a spouse who has done it before 'taints' both spouses, meaning between both spouses, it can only be done once.
Please read at CA. Gov: http://www.boe.ca.gov/proptaxes/faqs/propositions60_90.htm
And please get advice from a legal tax advisor.