California Code, Public Resources Code - PRC § 29728

“Primary zone” means the delta land and water area of primary state concern and statewide significance which is situated within the boundaries of the delta, as described in Section 12220 of the Water Code, but that is not within either the urban limit line or sphere of influence line of any local government's general plan or currently existing studies, as of January 1, 1992.  The precise boundary lines of the primary zone includes the land and water areas as shown on the map titled “Delta Protection Zones” on file with the State Lands Commission.  Where the boundary between the primary zone and secondary zone is a river, stream, channel, or waterway, the boundary line shall be the middle of that river, stream, channel, or waterway.