It's a G fare which should earn 100% miles on both UA and CO (although united.com appears slightly out of date with regards to G fares); if you can find inventory it looks like you can route around a little bit. Possible to do MIA-LAX-MIA in under 18 hours if you feel like the 12:30am or 1:30am LAX-IAH returns. Not sure how fast you can do LAX-MIA-LAX. One way fare in case you don't want a return. This has been coming and going for a few months now (to SFO at some points earlier this year).