California Code, Government Code - GOV § 56710

(a) The assessed value to be given land exempt from taxation or owned by a public agency shall be determined by the county assessor, at the request of the executive officer, in the same amount as the county assessor would assess that land, if the land were not exempt from taxation or owned by a public agency.

(b) The value given land held in joint tenancy or tenancy in common shall be determined in proportion to the proportionate interest of the petitioner in that land.

(c) The executive officer shall disregard the signature of any person not shown as owner on the most recent assessment roll being prepared by the county at the time the proponent adopts a resolution of application pursuant to Section 56654 or files a notice of intention to circulate a petition with the executive officer pursuant to subdivision (a) of Section 56700.4, unless prior to certification the executive officer is furnished with written evidence, satisfactory to the executive officer, that the signer meets any of the following requirements: