Carpinteria State Beach. See below:
"Near" is a relative term. There isn't much in and around LA proper, since real estate is much too expensive. Within 100 miles, you have a selection of campgrounds for tent camping. Try some of these campgrounds, listed roughly north to south). State campgrounds can be reserved at www.reserveamerica.com:
Refugio State Beach: North of Santa Barbara about 15 miles. This campground is right on the beach level, and has some spots just a few feet from the water. It’s a nice place, and it’s not too far from SB. However, one drawback it the freight trains: It is located at a bend in the RR tracks (most state beaches are right by some RR tracks, BTW), and the longer “piggyback” cars screech when they make the turn. It’s not a pleasant sound, but it only happens a couple times a day.
El Capitan State Beach: Practically next door to Refugio, 2 miles south. El Cap is on the bluffs above the beach, with many trees around the campsites. However, the trains here are much less obtrusive, because there’s no crossing (so no blasts from the horn), and the train is slightly below ground level at this point, as the tracks are dug into the hillside. This is my second-favorite campground.
Carpinteria State Beach: 12 miles south/east of Santa Barbara. My favorite beach is Carpinteria, which is rated at "The World's Safest Beach". There is plenty of beach for swimming or body surfing. There are some excellent tide pools on the south end of the beach, and some large natural tar seeps nearby, which is how the beach got its name (The Spaniards noticed that the local natives used the tar to make their canoes... the word Carpinteria basically means "wood shop"). Also, there are plenty of places to explore in the nice little town. There are fun local restaurants like the Spot (just look for the line of people on Linden Avenue), the Palms (where you cook your own steak), or Giovanni's Pizza (where they have excellent antipasto salad). There is even an old-fashioned candy store called Robitaille's (RO-bah-ties). Kids will also probably like the surf shop (Matt Moore's Rincon Designs), and Foster's Freeze... nothing like a ice cream cone on a warm afternoon. The trains go by, but it’s a minor inconvenience compared to the benefits. In fact, it’s a source of entertainment, since you can put a penny on the tracks and watch it get smashed flat by the train. Also, there is a train platform about 100 yards from the north end of the campground, which we have used when someone in our group hast to come late or leave early. Camping on the beach doesn’t get any better than Carpinteria, which puts you steps away from the sand and surf. Be sure to bring your bikes: It’s one of the favorite activities besides going to the beach. Just before dinnertime, the campground has more bikes moving than cars. This is probably the most family-friendly camping on the coast. However, you’ll need to plan well in advance: Sites book 6 months in advance, so you have to think of summer camping in the winter (Memorial Day weekend books November 1, for example).
McGrath State Beach, Ventura: This is a nice enough beach. Technically, you are on the beach, but it’s almost ¼ mile to the water over the dunes. And no trains to worry about.
Leo Carrillo State Park, Malibu: Note the name. Most people call it Leo Carrillo State Beach, but it’s on the inland side of PCH, and you can walk under PCH to get to the beach. Since the beach is covered with large rocks, it’s low on my list of favorite campsites.
Newport Dunes: : Located in Newport Beach, it’s the Cadillac of RV parks. You can tent camp here as well, but the park caters mainly to RV’s. The prices are 2-3 times that of the state parks. If I wanted to spend that much, I'd get a hotel room. www.newportdunes.com.
Doheney State Beach, Dana Point: This is one of the few campgrounds that have actual beachfront sites. There is a VERY nice park next door, and you are within walking distance of the Dana Point Harbor and shops. Just across PCH and the RR tracks, there is a condo development where you could pay hundreds per night to stay. Or, you could pay twenty bucks and camp right on the beach. The choice is yours. This is another one of my favorite spots for tent camping.
San Clemente State Beach: Located in the beach town of San Clemente, it is located on the bluffs overlooking the beach.
San Onofre State Beach: Unless you are a HARD CORE surfer, this is not a good place to camp. I camped here once, but never again. You are 10 feet from the RR tracks, 20 feet from I-5. If you're lucky, you get to be right next to the border checkpoint, with flashing lights all night. And it's ¼ mile walk to the beach. There are loud teens and twenty-somethings up late, and no ranger enforcement of quiet time. Great if you're a college-aged person and want to surf and party, but rotten for families.
South Carlsbad State Beach: Close to Legoland in north San Diego County. Located on a strip of land on the bluffs above the beach, it’s great for whale watching during migration season.
San Elijo State Beach: Located in Leucadia, in north San Diego County. Same as South Carlsbad, but with a few hookup sites if you have an RV.
Campland on the Bay: Private campground on the north end of Mission Bay, close to Sea World. Excellent location, lots of organized activities, but you pay for it. Full amenities here, like Newport Dunes.