A similar thing happened to my brother and I back in 2006, when we were doing the Cascade Loop in WA. After leaving Winthrop, Microsoft's Streets & Trips GPS software on my laptop put us on a road that was gradually ridden with trees. We finally decided to turn back after a full tree trunk was cutting off the road and the asphalt almost disappeared. I checked the map later. If we had pushed forward, we would have crossed the border to Canada in two hours max.