It used to be very senior. Fun facts: For a time in the early 2000's, every (100%) of the B737-200 F/O's lived in and were residents of the state of Alaska.
The number #1 Captain in the company lived in SEA but commuted to ANC until his death, while doing a walk around (RIP Tedrick). There were a handful of commuting Captains, but not many. Less than 10% as I recall. Then the 200 went away, the 400/NG showed up, the flying of the base changed and here we are.