Of the four lagoons in North County, I like running in the San Dieguito Lagoon the best. The other lagoons in North County are San Elijo (between Solana Beach and Encinitas), Batiquitos (between Encinitas and Carlsbad), and Buena Vista (between Carlsbad and Oceanside). And they are nice places to run too. Definitely worth checking out.
The lagoons can be a little bit snake-alicious, especially in the spring. That is why the San Dieguito is my favorite. First, I have never seen or heard a live snake in there, and second, the paths are wide (as wide as a car the whole way), so it would be easy to avoid one.
Creepy side-note: I have seen a dead snake in the San Dieguito Lagoon. Someone killed it and put it along side the trail and was probably filming reactions from some unseen vantage point. I am sure mine was one of the most hilarious: shrill scream, jump 10 feet in the air, land and sprint off as fast as I could. Turn around, realize the snake is not moving, reapproach the snake carefully for closer inspection, decide it is not worth it, and abort. Run off in other direction at base pace. You see the weirdest stuff running, right?
The San Dieguito Lagoon borders Del Mar and Solana Beach. After the inlet at Del Mar Dog Beach was dredged last September, and water filled the lagoon, it became a really pleasant place to run (a little bit desolate and dry before).
This route starts along the 101 at Via De La Valle. Proceeding south, and running against traffic along the 101, be on the lookout for a dirt path on your left, not too far after you cross the bridge. The dirt path runs between Sandy Pointe condos and the inlet that feeds the lagoon. This little dirt path will take you as far as the railroad tracks. This time of year, you can see the San Diego County Fair.
You'll have to cross the railroad tracks, so be careful and look both ways. Then you'll pick up the San Dieguito River Trail. This trail will take you as far as Jimmy Durante Blvd., which you will need to cross to get into the main part of the lagoon.
Once you are in the main part of the lagoon, you can relax and get your running groove on. A good trail map is here.
You'll pass the Del Mar castle where Tony Robbins used to live:
And I have seen a red-winged black bird every time I've run in the lagoon.
But I don't want to oversell here. It is not the most scenic of places. You do have to pass under the 5, behind the Albertson's strip mall, and you'll hear traffic noise from the 5 pretty non-stop. But it is pretty good for being in the middle of an urban area! The trails are really nice, it is not busy, and once you get east of the 5, there are a lot of birds singing and flying around. It is a nice alternative to running the 101 on a busy weekend morning!
When you get to the polo fields, turn around and head back.
Total Distance: 6.3 miles (out-and-back).
Parking: along Via De La Valle, Solana Circle, or Cedros.
Start / Finish: Via De La Valle and the 101 (Camino Del Mar).