I knew I had read it somewhere... In an article in the company site, they talk about fuel efficiency and steps taken to try and reduce fuel burn.
One of the things done (which didn't pan out) is:
"Flight operations also has looked at a number of ideas in recent months that have not panned out. One is removing the gravel guards from 737-200 jets, now that every airport Alaska Airlines serves is paved. “Our analysis showed that the cost of removing the guards exceeded estimated fuel savings,”"
I've never done a Red Dog flight but I thought I had heard that all of our fields were paved...