This is VERY tight, and I strongly advise you standby on a earlier LAX-SAN flight to gain an extra 30 min or so cushion time. You will literally have to go from one end of the airport to the other; you will arrive into the Commuter Terminal, and depart from Terminal 2 West. The primary way to get there is to take the red "interterminal bus" which stops at all terminals. You will first have to stop at Terminal 1, then Terminal 2 East, and then Terminal 2 West. Hopefully you don't have to wait too long for the bus. Timing is hit or miss, and less buses tend to run later into the evening. I'd imagine you could always pay for a cab to take you there, and can't cost much. Once at Terminal 2 West, you will need to reclear security. Make sure you get your US boarding pass in LAX so you don't have to go to the counter. And I would personally suggest you carry on baggage as I'd be surprised if the bags transfer in time. Good luck.