"At some point in their lives, homeowners are likely to consider selling the home they may have occupied for many
years, and downsizing to a smaller residence. Normally, a new home purchase means the County Tax Assessor
hits the jackpot under California Prop. 13’s rules, which re-assess real property and bump up property taxes with
each new change in ownership. However, following a 1986 voter initiative passed by a 77% vote, homeowners
over the age of 55 have the privilege of transferring the assessed value of their present home to a replacement
home.

As always, the devil is in the details. This article offers some basic instruction in the rules which apply to Prop 60,
and its companions, Prop. 90 and Prop 110, and also discusses two other types of transfers which may be exempt
from re-assessment."

http://g3mh.com/wp-content/uploads/2017/11/2017-Downsizing-FAQs.pdf