I decided overnight that I didn't like that I was so far East, so started looking at new locations. Then I came up with a new twist, reversed the direction of travel as into Seattle not out, which is actually easier to explain plotwise and looked for places where there'd been logging, which will handily meet all the needs of being both open and difficult to access. So now I'm putting the scene up in the Acme/Wickersham area. Still far enough out that they can justify using the helicopter, but the location makes more sense within the plot.

Additionally googled: Reforestation in clear cut forests.