In most states, and California is included, touching isn't legal. I don't think you're going to get picked up or kicked out if you touch their thighs or something while you're getting a lap dance (privatly) but you won't be... "touching" any other spots, like the ass or tits or whatever.

Granted, they usually end up rubbing themselves all over you and your buddies and your girlfriends if you've brought them... and everyone else. But you cant' just slap their ass or something, no.