California Revenue & Taxation Code
Cal. Rev. & Tax. Code § 5011
All or any portion of any assessment of state-assessed property heretofore or hereafter levied may, on satisfactory proof, be canceled by the board if it was made:
(a)
More than once.
(b)
Erroneously or illegally.
(c)
On improvements when the improvements did not exist on the lien date.
Source: official text