Comment by sbuttgereit

It's just market value.

> *SECTION 1. (a) The maximum amount of any ad valorem tax on real property shall not exceed One percent (1%) of the full cash value of such property. The one percent (1%) tax to be collected by the counties and apportioned according to law to the districts within the counties.*

(https://leginfo.legislature.ca.gov/faces/codes_displayText.x...)

At sales time basically the sales price establishes the assessed value for taxes.

Again, this isn't a precise reading, but the general idea.