being that your final destination is international and not domestic. Most of the time I fly international, they only check the passport on the final (international) leg of the flight. You are probably good to get off the plane in SLC, but I'd bring the passport just in case they require it in LAX.

Standard rules apply for hidden city tickets. As soon as you don't get on the last leg, they cancel the rest of your ticket, so it should be a one way ticket. And you can't check any bags.