Iron Man #21 (Vol 6)

I'm not sure... perhaps it was Utah.
Continuing from Iron Man / Hellcat Annual #1:

After his skirmish with a super-intelligent gorilla in New York City, Tony Stark boards a flight back to California for some respite. However, he discovers a high-altitude hijacker on the same flight, intent on stealing a briefcase of gold bullion. When the thief parachutes out at 30,000 feet, Tony suits up in his Iron Man armor and gives chase, only to be caught in the criminal's traps in the desolate Southwest wilderness. With his armor's flight systems compromised, Tony must track this skilled survivalist, who is hauling a fortune in gold, in the vast emptiness... and make it out alive. Can his technological might stand up to another's primal command of nature? Iron Man takes on the wild, featuring the debut of a new adversary: SWITCHBACK!

LEGACY #646

Key Facts:
First appearance of Switchback