There was some discussion about the shortest US domestic flight flown by a mainline carrier and not commuter.

Well, in the February issue of "Airways" magazine, there's an article about the AS 73M, flight 64, that goes ANC-JNU-PSG-WRG-KTN-SEA. The PSG-WRG flight is listed as 30 miles in AS' timetable, 20-22 minutes flight time. [Great Circle Mapper says 31 miles.]