Hey Wizard, as per your request, I though I'd provide you with a little insight regarding Blacks Beach. I have been going there since 1970, and I remember the 1972 California court case that set the precedent by stating that "simple beach nudity is not indecent exposure".
A few years ago, the City of San Diego prohibited nudity on their small portion of Blacks Beach at the south end.
However, the majority of Blacks is under the jurisdiction of the California State Parks. Although California State Law (see below) if very clear,the State Park rangers at Blacks operate under a policy known as the "Cahill" policy, named after a former Parks Director: "it shall be the policy of the Department that enforcement of nude sunbathing regulations within the State Park System shall be made only upon the complaint of a private citizen. Citations or arrests shall be made only after attempts are made to elicit voluntary compliance
with the regulations."
Since the people most likely to make a complaint are also the least likely to make an effort to get to a remote part of a state beach,those areas, including Blacks, have become clothing optional.
Regarding your recent personal experience regarding the sheriff and CPS, I know from my own observation and discussions with some of my nudist family friends, that no authority at Blacks has ever, or would ever, approach a nudist family and haul the kids off to CPS. Just today I talked to about 3 nude families who had children about the age of your children. They all were nude, and they told me they have never been hassled or told to get dressed at Blacks. In fact, the lifeguards patrol the beach regularly and do not even bat an eye at all the naked people.
Here is some more general law from both the Federal and State viewpoint. Katrina has also provided some in another post. I hope you can continue your research, but I hope some of this helps you in support of your actions.
Federal Land
There is no Federal law against nudity but neither is it a guaranteed right. This means that state, county and local laws can take precedence.
California State Law
CALIFORNIA CODES SECTION 314-318.6 (as of 6/2000): Every person who willfully and lewdly, either: 1. Exposes his person, or the private parts thereof, in any public place, or in any place where there are present other persons to be offended or annoyed thereby; or, 2. Procures, counsels, or assists any person so to expose himself or take part in any model artist exhibition, or to make any othe exhibition of himself to public view, or the view of any number of persons, such as is
offensive to decency, or is adapted to excite to or thoughts or acts, is guilty of a
misdemeanor.
Every person who violates subdivision 1 of this section after having entered, without
consent, an inhabited dwelling house, or trailer coach as defined in Section 635 of the Vehicle , or the inhabited portion of any other building, is punishable by imprisonment
in the state prison, or in the county jail not exceeding one year.
Upon the second and each subsequent conviction under subdivision 1 of this section,or upon a first conviction under subdivision 1 of this section after a previous conviction under Section 288, every person so convicted is guilty of a felony, and is punishable by imprisonment in state prison.
However, different localities havetheir own laws (notably Santa Barbara and Los Angeles Counties) and beach nudity will net you a citation and a fine with no questions asked.
State Parks
Section 4322 of Title 14 of the California Administrative Code regarding nudity in the state parks: No person shall appear nude while in any unit except in authorized areas set aside for that purpose by the Department. The word nude as used herein means unclothed or in such a state of undress as to expose any part of portion of the pubic or anal region or genitalia of any person or any
portion of the breast at or below the areola thereof of any female person.
All sections are misdemeanors which carry a maximum punishment of 90 days in jail
and/or $1,000 fine.