This is a paved bike path that starts almost at the ocean in Oceanside and goes up the San Luis Rey River along a levee. I don't think I rode the whole path, because when I got to a residential area, the path suddenly ended, but signs indicated it might start up again after you ride along a street for a short distance. That occurs about 8 miles ride from the ocean. The miles are marked on the path's pavement. (I used my odometer, but also recorded round trip mileage, riding from my son's house at Camp Pendleton.) I rode my mountain bike, but road bikes or roller blades are fine too. Or you can walk, but it would be deadly boring, at least for me. There were quite a few people out there enjoying it. Lots of roadies and runners.
A fire started about 5 minutes after I had passed a road crossing. I stopped for a break and was surprised to see black smoke billowing up. The road crossings have bypasses for the trail that go under the river bridges, so you don't have to cross traffic. Anyhow, this fire must have started quite suddenly right after I passed that area. I could see it back there, but didn't feel like riding back to see what it was.
Although this path has a lot of natural beauty, it is quite urban as well, and the further inland you go, the more graffiti there is. This area used to all be rural when I was a kid, but so much has changed in 40 years. I don't want to belabor that point, but it's always in the back of my mind. Once upon a time I tried to raft the San Luis Rey River during the spring runoff, but that was in another lifetime...with a good friend who is now long dead. We grounded on sandbars so frequently that we had to give up, hitching back to the car which we had parked way up by Pala somewhere. No casinos back then. No graffiti, either. No I-15.
The history of Spanish settlement of this area goes back to the 1700's. It's fascinating. You can visit the old Spanish mission: http://www.sanluisrey.org/