Cal. Welf. and Inst. Code § 5202
The person or agency designated by the county shall prepare the petition and all other forms required in the proceeding, and shall be responsible for filing the petition. Before filing the petition, the person or agency designated by the county shall request the person or agency designated by the county and approved by the State Department of Health Care Services to provide prepetition screening to determine whether there is probable cause to believe the allegations. The person or agency providing prepetition screening shall conduct a reasonable investigation of the allegations and make a reasonable effort to personally interview the subject of the petition. The screening shall also determine whether the person will agree voluntarily to receive crisis intervention services or an evaluation in his own home or in a facility designated by the county and approved by the State Department of Health Care Services. Following prepetition screening, the person or agency designated by the county shall file the petition if satisfied that there is probable cause to believe that the person is, as a result of mental disorder, a danger to others, or to himself or herself, or gravely disabled, and that the person will not voluntarily receive evaluation or crisis intervention.
If the petition is filed, it shall be accompanied by a report containing the findings of the person or agency designated by the county to provide prepetition screening. The prepetition screening report submitted to the superior court shall be confidential and shall be subject to the provisions of Section 5328.
Ca. Welf. and Inst. Code § 5202