San Felasco is supposed to be sort of flat, tame, sandy singletrack. There are some trails of mixed quality called the Powerlines, but they are on provate property and the last time I was there, we had a nasty run-in with some well-concealed barbed wire.
Santos, also called Barge Canals, has some very nice quarry riding. There are two trailheads, one which is the one everyone seems to use and starts off at some singletrack, the other starts off at the beginning of a nice, very technical quarry ride with some makeshift stunts built in.
Not far from there there is another set of trails called Hardrock, which is also fast, technical rock quarry kind of stuff with some steeper climbs not cleanable on an SS.
Dunno about where you can find a bike to rent, but give Chain Reaction a call, there are some SS guys there. The number is 373 4052.
Tim