California Code, Government Code - GOV § 170

To give greater precision to the boundary of the State of California as defined in Article XXI of the Constitution, it is hereby declared that the part of the boundary which is described as “running in a northwesterly direction and following the direction of the Pacific Coast to the forty-second degree of north latitude,” and as “including all the islands, harbors, and bays along and adjacent to the coast,” runs and has in the past run three English nautical miles oceanward of lines drawn along the outer sides of the outermost of the islands, reefs and rocks along and adjacent to the mainland and across intervening waters;  and where there are harbors, but no such outlying islands, reefs and rocks, it runs and in the past has run three English nautical miles oceanward of lines drawn in front of the harbors along the outermost works and installations thereof, and, in the case of all bays (including inlets and estuaries) three English nautical miles from lines drawn from headland to headland across the mouth of each bay, inlet and estuary, regardless of the length of the lines.

Where there are no outlying islands, reefs or rocks and no harbors or bays or inlets or estuaries, the boundary runs and has in the past run three English nautical miles oceanward of the lowest low-water mark on the shore.