Originally Posted by WHBM

One of them, I would guess, is Riverton WY. Strangely, this small point used to be a Frontier hub, going back to the 1950s when Frontier was an all-DC3 operation, and was due to the US Mail contracts. Twice a day in those early days, Frontier flights had long come in from Denver, Salt Lake and Billings, via a whole string of intermediate points, exchange the mail in a few minutes, and then move on