I just came back from family roadtrip to see Yellowstone National Park and Mount Rushmore. Gas prices were much less in every state we passed through (Idaho, Montana, South Dakota, Wyoming) compared to WA. Including the gas stations INSIDE THE PARK. I filled up our non- roadtrip car for $4.65/gal a couple days before we left at our Costco. Several days later while inside Yellowstone the gas was barely over $4/ gal. I'll have to revise this after I get to go through my receipts, but that is just asinine. It's cheaper to fill up one of the most heavily visited places in the country than near my own suburban home.
*Update: $4.20/gal near our hotel in West Yellowstone on 7/16. $4.30/gal at Canyon Village inside Yellowstone on 7/18 Finally, $4.00/gal at West Yellowstone on 7/20. Here at home in Pierce County WA, $4.70/gal at Costco on 7/27. So at Yellowstone where you know they will charge more for convenience and the location, it's STILL cheaper than at home.