in the 1970s UA operated a mainline FAT-MCD flight (56 miles apart by car) - the flight continued on to SFO. If (fading) memory serves, it used either a B-727 or B-720.

Not open to the public, but as a non-rev I took some EWR-LGA flights on CO. The "flight" was essentially a way to ferry an aircraft over to LGA so that it could operate a revenue flight.