I used to live in San Clemente, the closest Hot Springs in the area are out in the desert,up near San Bernadino Deep Creek, or up the coast towards San Louis Obispo, There are a few out toward the Salton Sea, if you don't mind soaking with the old people the best place is the Fountain of Youth RV Park which has a unique hot steam room, but it will be so hot outside you won't want to soak. My favorites are the freebie off I-8 near El Centro, the Hot springs in Anzo Borrego, (pay per use at a campground), and Deep Creek near San Bernadino. There used to be a Hot Spring East of San Juan Capastrano, but it closed down many years ago.If you go in late June to Deep Creek watch out for the rattlesnakes and the wierdos.

Agua Caliente in the Anza Borrego Desert is one. It's a little place on the side of the highway with two pools. I don't remember the road names but if you leave Julian down the hill towards the desert then take a right at the first highway you come to. You will be heading south, towards the border, and I believe it will be about 20 miles on the right hand side. If you hit the area with all the motorcycles & ATV's you've gone about 5 mile too far. I also went to this other place in the Anza Borrego that was at some sort of club or resort. They had a huge olympic sized pool that had some really powerful water. It wasn't very crowded when I was there, just a few Elders floating around. Unfortunately I can't remember the name of it.

Hope this helps and have fun on your travels.