UA leaves from terminal 7, AF leaves from the intl terminal. which is between #3 & 4 on the loop.

work with your agent to ensure that you can check in across the entire itinerary, otherwise, you'll be subjected to having to re-check in for your UA flight.

security is crazy at LAX, if you're on a first class ticket to tuscon or a SA gold member, they have a special line for you at UA, but to clear immigration, re-check bags and clear security should be ok for you.

good luck!