Cal. Rev. & Tax. Code § 732

Each year between the first day of January and the last day of July, upon valuing the nonunitary property of an assessee, the board shall mail to the assessee at its address shown in the records of the board a notice stating the amount of the assessed value of the assessee’s nonunitary property. The notice shall advise the assessee that a petition for reassessment of the nonunitary property may be filed, not later than September 20 of the year of the notice, at the headquarters of the board in Sacramento.