And at night a GPS unit is a good idea. Daytime is just a bad idea I think, unless it's an unusually cool day for August, then maybe a 5:00 am start would be okay.
A better idea: you can do San Gorgonio, the tallest mountain in Southern California at 11,500 feet.
http://members.boardhost.com/sgva/
The main issue with that is avoiding thunderstorms which usually happen late morning and afternoon. Above tree line you're very exposed as you are the tallest thing around.
