Thank you for the information. Unfortunately, these are Q fares, which only count 50%, according to
http://www.flyerguide.com/wiki/index.php/Challenge_(AA).
However, the round trip of SFO-MIA-LIM-MIA-SFO is 20,400 actual miles, so it appears that this one round trip could get me Platinum status. I have never done a challenge on any airline, but this may be my first.