There is no Y other than 0 which would be allowed under the California Constitution (Prop 13 limits ad valorem property taxes to a fixed 1% of allowed tax basis value, as well as limiting the annual increase in tax basis value, local entities can't add selective additional ad valorem property taxes on top of this), and there is no X which would make them sell which would not be regulatory taking without compensation in violation of the 5th Amendment to the US Constitution (as well as provisions of the State Constitutions.)