UPDATE: I have removed the directions to this spot. Like usual, people (douches) are going out here and disrespecting this spot and its surrounding. Sorry folks!
Personal Experience: First off, they don't call it Hellhole Canyon for nothing. This place is hot (I don't recommend going in the summer) it's filled with ticks, brush which rattlesnakes like to hide in, poison oak and the hike is rather bland. Don't go unless you're really interested in finding these homes because the hike is not that fun! And please come prepared with a lot of water, food (in case you get lost) and all other proper safety gear for hikes that can go bad. With that said, this literally appears to be an abandoned commune. There are children's rooms with drawings on the walls, kitchens with pots, pans and canned food, letters, a well, work station and SO much more! I am dying to know the history of this area but after speaking to the people who run the Hellhole Canyon website and the Valley Center historians, nobody seems to know!