The closest place that I ever found was Box Canyon which is just north of Ramona off of Magnolia Rd about 5+ miles once you're on the dirt road and its a bit of a hike down to River Quarry !!!
Not that I am aware of. Pinecrest retreat has a pool, but they only allow guest if they are with a swim club member. Nearly all San Diego lakes forbid swimming (including lake hodges) as they are drinking water reserves.
Lake Hughes? (Not very close.)
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