Steve Foley writes:

Getting back to the point, I don't see any airways 20 miles southeast of
Aspen. What was your route?

ETL.V68.MTJ.RIL.DBL

I wasn't flying an airway in the 172. I prepared a route that avoided the
high mountains to the east.

I have since flown IFR via ETL.V68.MTJ.V361.DBL at 12000 in the Baron, with no
problems (although KASE was VFR at the time).

I also saw (I think) in a post that you leaned the mixture prior to
take-off. Did you continue leaning as you climbed?

I leaned the mixture for take-off because of the altitude. Held the brakes,
full throttle, adjusted mixture for 10° rich of peak. I did lean it slightly
more during the flight, but there isn't much difference in mixture between
9000 and 12000 feet. I always lean the mixture for peak EGT and then back off
5-15 degrees.