I'd say "Fligh****ch, experimental 3642 near Ogden (or nearest known
position so they know which transmitter to reply with)"
Errr, Flight Service (often on 122.2 - both transmit/receive)? Flight
Watch (122.0 - only, AFAIK) is for weather advisories.

Dang. Either way, I missed. My guess would be 121.5...

Bartek