Cal. Code of Civil Procedure - CCP § 837. Section 837.
(a)
A groundwater sustainability agency for the basin or a portion of the basin may intervene in a comprehensive adjudication conducted pursuant to this chapter.
(b)
A city, county, or city and county that overlies the basin or a portion of the basin may intervene in a comprehensive adjudication conducted pursuant to this chapter.
(c)
The court shall allow any person to intervene in a comprehensive adjudication conducted pursuant to this chapter upon an ex parte application that demonstrates that the person holds fee simple ownership in a parcel in the basin, or extracts or stores water in the basin. A person filing an ex parte application pursuant to this subdivision shall give notice to the plaintiff consistent with the California Rules of Court.
(d)
A person may apply to intervene in a comprehensive adjudication conducted pursuant to this chapter pursuant to Section 387.