San Elijo State Beach

Yes it's busy, yes the Coaster and Amtrak trains go by frequently blaring their horns (which are awesome options to get to the heart of San Diego, btw) but this is still one of our favorite spots. It's beautiful on the bluffs and you can access one of the very few dog beaches right from the campground (at the southern end) -- it's a fairly small area but you could also opt to cross the bridge and all of that long stretch of beach is also dog friendly.
We also LOVE Cardiff. The Seaside Market is spendy but has excellent produce, a great beer and wine selection, and a fantastic deli and seafood counter. I love shopping at the Rancho Coastal thrift store which supports the humane society. VG Donuts is right there and Best Pizza and Brew -- two great spots. And we've been to the Cardiff vet, all right there within walking distance to the campground. In the huge sprawling area that is San Diego County, we love to be able to walk and bike to the places we love. Biking to Encinitas is easy and fun, with beautiful ocean views and so many good eateries there.
Back to the campground -- we have found that we prefer the southern end when possible, to be close to the dog beach, the middle section tends to be the loudest and busiest, and the northern section is much more quiet. There are several 'back row' sites with decent views of the ocean if you're not right behind the bathroom building like we were in site 133 -- site 132 would have had much better views.
Catch the sunset, bike to breweries, and just slow down and enjoy the chill surfer vibe of this small beachside community.
When we were here in late January, the camp store was closed. The laundry room was also totally deconstructed -- not sure if that was for renovations or if it's always closed in the winter season. Nearest laundry we found was in Encinitas, Jolly Clean Giant, didn't love that you had to use a laundry card to pay (no coins) which they were actually out of, but a woman working there let me borrow hers.

I made reservations 6 months in advance to get a site overlooking the water. Site 145 accommodated our 34' foot Airstream, but did require some up on curb driving, there is a loop in front of this spot which allows for more room to back up. The site was big enough, but will test your driving skills, hey it's worth it to camp on the beach! Site 145 is also on the end so there is less traffic going by your site. There are fire pits and picnic tables on each site. The facilities were clean. The camp is right on the beach, but there is train and traffic noise at night.
The check in was friendly and fast. There is the cute little town of Cardiff by the Sea across the highway, with a coffee shop and breakfast taco place within walking distance, also a grocery store (Seaside Market). The camp store in the park was well equipped with supplies also. This park was definitely popular among the locals, you can tell there were a lot of regulars.

The location on the bluff is very cool. The sites are mix of dirt and asphalt. It’s a pretty good location for visiting all of the San Diego area attractions. The problem with the park is the noise (PCH and commuter trains) and the number of day use people that come off PCH. All of the beach goers park on PCH and then walk through the campsites. We were there during the offseason and during the week (weather was amazing) and it felt packed. I can’t imagine what the summer is like. Just plan on extra noise and lots of people!

I don't need to reiterate what many have already said in previous posts about the people, the noise & busyness of this location. That is all true. So are the comments on the beauty. This is a fabulous location with great amenities at the grounds as well as within walking distance. For me I would only give this three stars because of the noise. Not only are there trains but in the evening it was a bit of a party scene with many groups getting loud with their music and festivities. This may be personal prefence and if that sort of thing is your scene than you'll love it and give it 5 stars.

The grounds were very clean and well kept.

Note: some of the sites are VERY hard to get a trailer into because of how narrow the road is and how closely packed all the sites are. I actually had to turn around and drive the wrong way down a one way street to get an angle on my site that i could back in.

There's a lot going for San Elijo State Beach.

Yes, there's trains that come at all hours of the day and are so loud and sometimes shake the ground so much that it feels like they're coming through the campground.
Yes, it's a very busy campground with surfers, trailers, dogs, etc. coming and going most of the day.
Yes, it's right on a major through-way with heavy traffic most of the day.
Yes, it's $50 a night for a dry oceanfront site.
Yes, you need to book your campsite 6 months in advance the minute that it's available, even for the "off season" (seriously, they all filled up within a few minutes of becoming available).
Yes, getting into the campground is a pain in the butt as it's only accessible from the North, there really isn't any great turnarounds for large trailers, and the access lane is very narrow and you are guaranteed to curb it if you have a large trailer.

None of that really matters because you're not going to get a better oceanfront view in Southern California without being end-to-end or shoulder-to-shoulder at smaller "campgrounds" or camped along the road. Huge Pelicans fly within 20ft of your window many times an hour. Sitting in my Airstream with the rear window open and working all day has been fantastic and inspirational, and walking along the warm-ish sand barefoot in the afternoons after a day of conf calls is recharging. All this being said the non-Oceanfront campsites aren't spectacular, and the rear ones back onto the road. Book early to secure a spectacular oceanfront spot!

We were a few minutes late getting to the booking page and managed to get the last available oceanfront site - number 001 - but we did get to mooch off the neighboring camp store//taco stand wifi and avoid running our Verizon plans for YouTube. :)

We originally planned to only stay one week, but luckily snagged a second week last minute as the California fires prevented us from moving on to our next destination. This campground was beautiful. You can’t really beat the proximity to the beach and ocean sunsets. It was a short walk to the grocery store and post office in Cardiff by the Sea- lots of restaurants and surf shops too. My only complaint is that there isn’t a gate closing the campground at night. There was quite a bit of non-camper foot traffic. The laundry was reasonable and convenient, but closed at 6pm to “keep homeless people from trying to sleep there”, or so said the gift shop attendant. It’s also close to the train tracks, but we got used to the noise rather quickly. We really enjoyed our stay, the park rangers were full of great local recommendations, and we overall felt safe. We had full E/W/S sites in both spots so we didn’t use the campground showers. Cell service was great without a booster on ATT and Verizon.

Like everyone else has said, between the trains, the kids, the tourists, it's what I would normally call a nightmare, but there's something about being camped right there next to the beach that sort of makes it okay. We came in on a Sunday during spring break without a reservation, and by some miracle got the one open spot because they were doing maintenance on it. FYI if you happen to get in with a reservation and want to stay longer than one night you will need to get up early to get in line, they advised us to get in line at 6am, this was overkill as nobody else showed till 7, you must physically lineup next to the entrance booth, at 8:15 they write down your names in the order you arrived, then you come back at 9:15 to see if they have a spot for you, and you have to do this every day, no multiple days allowed. Plus, you have to make reservations 48 hours out, so I would not recommend this place without a reservation, you can get in but it's a huge pain. The bathrooms were horrendous, otherwise fairly clean.