It ranges from business casual to more dressy (e.g. wearing a suit). For guys, a dress shirt and slacks will do, tie is optional. Don't wear jeans and a t-shirt (unless you're a Ph.D. in physics, then you can probably get away with it...). You should be a little more dressy (jacket and tie) if you're presenting or meeting/greeting, as stephew outlined. If you're interviewing, then a conservative suit is recommended.
Since the meeting's in LA, you're expected to wear chic sunglasses at all times, even while indoors, and even if you're presenting. 😎
Basically they run a loop. Should stop by your hotel every 15 min or 30 min or so during peak times, less often offpeak. You should get a list of the route pickup/dropoff points and schedule with your registration packet.