California Code, Water Code - WAT § 10723

(c)(1) Except as provided in paragraph (2), the following agencies created by statute to manage groundwater shall be deemed the exclusive local agencies within their respective statutory boundaries with powers to comply with this part:

(2) An agency identified in this subdivision may opt out of being the exclusive groundwater management agency within its statutory boundaries by sending a notice to the department, which shall be posted on the department's Internet Web site within 15 days of receipt. If an agency identified in paragraph (1) opts out of being the exclusive groundwater management agency, any other local agency or combination of local agencies operating within the statutory boundaries of the agency that has opted out may notify the department pursuant to Section 10723.8 of its decision to be the groundwater sustainability agency.

(3) A local agency listed in paragraph (1) may comply with this part by meeting the requirements of Section 10733.6 or opting to become a groundwater sustainability agency pursuant to this section. A local agency with authority to implement a basin-specific management plan pursuant to its principal act shall not exercise any authorities granted in this part in a manner inconsistent with any prohibitions or limitations in its principal act unless the governing board of the local agency makes a finding that the agency is unable to sustainably manage the basin without the prohibited authority.