California Code, Water Code - WAT § 12924

(a) The department, in conjunction with other public agencies, shall conduct an investigation of the state's groundwater basins.  The department shall identify the state's groundwater basins on the basis of geological and hydrological conditions and consideration of political boundary lines whenever practical.  The department shall also investigate existing general patterns of groundwater extraction and groundwater recharge within those basins to the extent necessary to identify basins that are subject to critical conditions of overdraft.

(b) The department may revise the boundaries of groundwater basins identified in subdivision (a) based on its own investigations or information provided by others.

(c) Notwithstanding Section 10231.5 of the Government Code, the department shall report its findings to the Governor and, in compliance with Section 9795 of the Government Code, the Legislature in years ending in five.