Cal. RTC § 3365

(a) After the first publication of the notice and not less than 21 days nor more than 35 days before July 1, the tax collector shall send by registered mail to the last assessee of the tax-defaulted property at his or her last known address a notice of default and power to sell the property for nonpayment of taxes. The tax collector shall make a reasonable effort to ascertain the address of the last assessee of the tax-defaulted property, including, but not limited to, an examination of the assessment of this property on the rolls beginning with the year of delinquency to and including that of the last equalized roll, an examination of the most recent telephone books in the county in which the tax-defaulted property is located, and an examination of the telephone book covering the area of the last known address of the last assessee.

(b) Any failure of the tax collector to make a reasonable effort to ascertain the address of the last assessee as required by this section shall not affect the validity of any subsequent sale to satisfy the lien of unpaid taxes.

(c) If the property subject to the notice required by this section is the subject of a bankruptcy proceeding, the notice shall constitute a “notice of tax deficiency” pursuant to Section 362(b)(9)(B) of Title 11 of the United States Code.