Jim, If you look at the San Diego County Sheriffs No Shoot Map and their regulations they end in most cases at the edge of the Pacific Ocean. I have had numerous discussions with Game Wardens about this due to hunting Sea Ducks. They are always really awesome and just say make sure you are outside the Sheriffs No Shoot Zone and follow DFW guidelines/Laws for occupied dwellings. Shooting regulations are run by the county not the state so there is no reason that you should need to be 3 miles out (aka federal waters).
Now in addition there is obviously the issue of whistleblowers thinking they are doing right yet are being ignorant of the laws. So while it is legal to shoot as little as 150 yards off of Mission Beach it doesn't mean you are not going to end up with a huge headache over it. Both San Diego Sheriff and DFW deem over 150 yards a legal, reasonable distance from any
occupied dwelling house, residence, or other building or any barn or other outbuilding inside of Unincoporated San Diego. (Section 33.101.B of the San Diego County Code of Regulatory Ordinances).
http://www.sdsheriff.net/documents/shooting_map.pdf
Mike, What tells you that you cannot carry within a certain distance of shore? There is no Map that I have ever seen saying you cant carry within a certain distance of shoreline or anything like that that I am aware of. It is all about Concealed Weapons Laws and your right to carry. The shoreline isn't a post office or a school so there should be zero issue if everything else checks out if you possess a CCW or you are using the Hunting/Fishing clause.
Now obviously If I am wrong i would love to know (and this is definitely possible). I haven't looked much into CCW stuff since I decided the run around with SD County was no longer worth it and gave up on they way they issue them. I will instead wait until i can leave this anti-firearm state to hold a CCW and in the meantime continue to use clauses such as the Place of Business and Hunting/Fishing to aid in carrying on my person.